1
What is a compass needle?
💡 Hint:
Its two ends point north and south.
Explanation:
The needle is a small bar magnet. The end toward the north is the north pole.
Class 10 · Science · Chapter 12 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Magnetic Effects of Electric Current
Magnetic Effects of Electric Current
How to use this page:
1. Read — Activity 12.1 compass · 12.2–12.3 field lines · 12.4–12.5 straight wire · 12.6 coil · 12.7 force, diagram, worked example, board tip
2. Check — each lesson has its own questions; the number follows the lesson
3. Mastery ★ — all of that lesson correct. Redo the wrong ones
4. Use the right-hand rule figure — the thumb points along the current and the fingers curl along the magnetic field.
In NCERT 2026-27 this is chapter 12. In the older Bihar book the same topic is chapter 13. Progress stays in this browser.
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- 1 The compass and a straight wire — Activity 12.1
- 2 Field lines — Activities 12.2 and 12.3
- 3 A straight wire and the right hand — Activities 12.4, 12.5
- 4 A circular coil — Activity 12.6
- 5 The solenoid and the electromagnet
- 6 Force on a conductor — Activity 12.7
- 7 Electromagnetic induction and Fleming right hand
- 8 The domestic circuit, the fuse and AC–DC
- Chapter winner — every lesson at mastery ★
🎬 Shorts
This chapter has no Short on the channel yet, so ten empty cards are not shown. The notes, diagrams and checks are complete.
📄 PDF download — notes + answer key
The compass and a straight wire — Activity 12.1
दिक्सूचक और सीधा तार — क्रियाकलाप 12.1 · NCERT opening of Chapter 12 · Activity 12.1
The needle is itself a small magnetNotes
A compass needle is a small bar magnet. The end that stays toward the north is the north pole and the end toward the south is the south pole. Like poles push apart and unlike poles pull together.
The needle turns near a bar magnet because the magnet has a field around it, a region where its force can be detected.
Activity 12.1 — the needle turns as soon as the key is insertedActivity
Place a thick straight copper wire between X and Y of a circuit, perpendicular to the plane of the paper. Keep a small compass horizontal near it and note the needle. Insert the key in the plug so that a current flows.
The needle turns. The current in the copper wire has produced a magnetic effect. Electricity and magnetism are linked.
Worked exampleExample
Question: Why does a compass turn near a bar magnet?
Answer: The needle is itself a small magnet. The field of the bar magnet exerts a force on it, so the needle settles in a new direction.
Oersted, 1820
Hans Christian Oersted saw in 1820 that a compass turns when a current flows in a nearby metal wire. The unit of magnetic field strength called the oersted is named after him.
10-second revision
- A compass needle is a small bar magnet
- A metal wire with current produces a magnetic field
- Like poles repel, unlike poles attract
Board tip · BSEBBoard tip
In an objective item the needle turns because of the field, not because the wire became hot.
Board tip · CBSEBoard tip
In a reason item write both Oersted name and the point that the effect stops when the current stops.
Check your understandingall correct = mastery ★
2
A nearby compass can turn when a current flows in a metal wire.
Explanation:
True — this is Activity 12.1 and Oersted observation.
3
What happens between like poles?
💡 Hint:
North-north or south-south.
Explanation:
Like poles repel. Unlike poles attract.
4
The unit of magnetic field strength called the oersted is named after ______.
💡 Hint:
The 1820 discovery.
Explanation:
The unit is named the oersted.
5
In Activity 12.1, why does the needle turn after the key is inserted?
Model answer (board format)
When the key is inserted a current flows in the copper wire. That current produces a magnetic field around the wire. The compass needle, being a small magnet, turns in that field.
Check your answer:
Field lines — Activities 12.2 and 12.3
क्षेत्र रेखाएँ — क्रियाकलाप 12.2 और 12.3 · NCERT 12.1 · Activities 12.2, 12.3
Activity 12.2 — the pattern of iron filingsActivity
Fix white paper on a drawing board. Place a bar magnet in the middle. Sprinkle iron filings around it. A salt sprinkler helps. Tap the board gently.
The filings settle into a pattern. The magnet exerts a force around itself. The region where this force can be detected has a magnetic field. The lines along which the filings settle are field lines.
Activity 12.3 — draw a line with the compassActivity
Mark the boundary of the magnet. Place the compass near the north pole. The south pole of the needle points toward the north pole of the magnet and the north pole of the needle points away. Mark both ends.
Move the needle so that its south pole sits where the north pole just was. Continue until you reach the south pole of the magnet. Join the marks with a smooth curve. That is one field line. Draw more. The deflection grows as you move toward the poles.
Five properties of the linesNotes
The direction of the field is the way a free north pole would move. So outside, the lines leave the north pole and meet at the south pole. Inside the magnet the direction is from south to north. The lines are closed curves.
Where the lines are crowded the field is strong. No two lines cross each other. If they did, the needle at that point would have to point two ways, which cannot happen.
| Place | Direction |
|---|---|
| Outside the magnet | North to south |
| Inside the magnet | South to north |
| Crowded lines | Stronger field |
| Two lines | Do not cross |
Worked exampleExample
Question: Why can two field lines not cross?
Answer: At the crossing the field would have two directions. A compass shows only one direction at a time. So a crossing is not possible.
10-second revision
- Outside N to S, inside S to N, lines are closed curves
- Crowded lines show a stronger field
- Two field lines do not cross
Board tip · BSEBBoard tip
If the outside direction is asked, write north to south. The inside direction is the reverse, so write it on its own line.
Board tip · CBSEBoard tip
In a reason item do not stop at “they do not cross”. Finish the reason about the needle having one direction.
Check your understandingall correct = mastery ★
1
Outside a bar magnet, field lines go which way?
💡 Hint:
The way a free north pole would move outside.
Explanation:
Outside, the lines go from the north pole to the south pole. Inside, the direction is from south to north.
2
Two magnetic field lines can cross each other.
Explanation:
False — at a crossing the needle would have to show two directions.
3
Where field lines are crowded, the field is ______.
💡 Hint:
Near the poles the needle turns more.
Explanation:
Crowded lines show a stronger field.
4
How is the direction of a magnetic field line fixed?
Model answer (board format)
The direction is the way a free north pole placed at that point would move. Outside, this is from north to south. The lines are closed curves, because inside the direction is from south to north.
Check your answer:
A straight wire and the right hand — Activities 12.4, 12.5
सीधा तार और दायाँ हाथ — क्रियाकलाप 12.4, 12.5 · NCERT 12.2.1–12.2.2 · Activities 12.4, 12.5
Activity 12.4 — reverse the current and the needle reversesActivity
Connect a long straight copper wire, two or three cells of 1.5 V and a plug key in series. Place the wire parallel to the compass needle and over it.
If the current flows from north to south, the north pole of the needle moves toward the east. Swap the cell terminals so the current flows from south to north. The needle now moves toward the west. Reversing the current reverses the field.
Activity 12.5 — concentric circles, distance and currentActivity
Take a 12 V battery, a rheostat, an ammeter of 0–5 A, a key and a thick copper wire. Pass the wire through the centre of a rectangular cardboard, normal to it. The cardboard must not slide. Sprinkle iron filings, keep the current fixed and close the key. Tap gently.
The filings settle in concentric circles around the wire. These are field lines. At a point P the north pole of a compass gives the direction. Reverse the current and the circles reverse too.
Increase the current and the deflection grows — the field is stronger. Move the compass farther, to a point Q, and the deflection falls. The field decreases as the distance increases, and the circles get larger.
The right-hand thumb ruleNotes
Hold the straight current-carrying wire in the right hand so that the thumb points along the current. The fingers then curl around the wire in the direction of the field lines. This is also called Maxwell corkscrew rule: drive a corkscrew in the direction of the current and the twist is the direction of the field.
For a current coming out of the page (a dot at the centre) the fingers curl anticlockwise. If the current goes in (a cross at the centre) the direction becomes clockwise.
Worked example — Example 12.1Example
Question: A current in a horizontal power line flows from east to west. What is the direction of the field at a point directly below the wire and at a point directly above it?
Answer: Point the thumb west. Viewed from the east end, the field turns clockwise in a plane perpendicular to the wire. Viewed from the west end, it is anticlockwise. The same turn applies both above and below. Reverse the current and the turn reverses too.
10-second revision
- With current north to south, the north pole of the needle moves east
- The field grows with current and falls with distance
- Thumb is current, fingers are the field
Board tip · BSEBBoard tip
Learn the direction pair of 12.4: current north to south, needle to the east. Reverse the current, needle to the west.
Board tip · CBSEBoard tip
CBSE asks the dot and the cross in a figure. A dot is out of the page and is anticlockwise with the right hand.
Check your understandingall correct = mastery ★
1
What is the magnetic field near a long straight wire like?
💡 Hint:
The iron filings of Activity 12.5.
Explanation:
The field is concentric circles. The circles get larger as the distance grows.
2
Increasing the current in the wire decreases the field at a point.
Explanation:
False — a larger current increases the deflection, so the field is stronger.
3
The thumb of the right hand shows the direction of the ______.
💡 Hint:
The fingers belong to the other quantity.
Explanation:
The thumb is along the current and the fingers along the field.
4
If the current is from north to south, which way does the north pole of the needle move?
💡 Hint:
The first case of Activity 12.4.
Explanation:
For a current from north to south the north pole moves east. When the current is reversed it moves west.
5
Why does the deflection decrease when the compass is moved away from a straight wire?
Model answer (board format)
The magnetic field of a given current decreases as the distance from the wire increases. So the deflection of the needle decreases too. The circles of the field lines get larger farther from the wire.
Check your answer:
6
Around a current coming out of the page the field is anticlockwise.
Explanation:
True — if the right thumb points out of the page, the fingers curl anticlockwise.
A circular coil — Activity 12.6
वृत्ताकार कुंडली — क्रियाकलाप 12.6 · NCERT 12.2.3 · Activity 12.6
At the centre of a loop the lines look straightNotes
The field of a straight wire falls as the distance grows and the circles get larger. Bend the wire into a circular loop and the large circles of each small piece look like straight lines at the centre.
Use the right hand. Every part of the loop adds its field in the same direction inside the centre. If there are n turns, the field is n times the field of one turn, because the current in every turn has the same direction.
Activity 12.6 — a circular coil on cardboardActivity
Take a rectangular cardboard with two holes. Insert a circular coil of many turns through the holes, normal to the cardboard. Connect the ends in series with a battery, a key and a rheostat. Sprinkle iron filings, plug the key and tap gently.
The filings show the pattern of the magnetic field of the coil. Near the centre the lines are crowded and nearly straight.
Worked exampleExample
Question: A circular loop lies on a table and the current is clockwise as seen from above. What is the direction of the field inside and outside the loop?
Answer: Curl the fingers of the right hand clockwise. The thumb points down into the table. So the field inside the loop is downward. Outside, the field returns upward.
10-second revision
- At the centre the field lines look nearly straight
- The field of n turns is n times the field of one turn
- A clockwise current gives a downward field inside
Board tip · BSEBBoard tip
Write the n-times sentence with the reason: the current in every turn adds in the same direction.
Board tip · CBSEBoard tip
In a clock-direction item curl the fingers first, then read the thumb as into the page or out of it.
Check your understandingall correct = mastery ★
1
How large is the field at the centre of a coil of n turns, compared with one turn?
💡 Hint:
Each turn adds in the same direction.
Explanation:
The field of n turns is n times the field of one turn.
2
At the centre of a circular loop the field lines look nearly straight.
Explanation:
True — the arcs of the large circles look straight at the centre. At the centre of a long coil they are parallel straight lines.
3
Inside a loop on a table with a clockwise current, the field points ______.
💡 Hint:
The thumb is fixed by the curl of the fingers.
Explanation:
For a clockwise current the field inside is downward. Outside it is upward.
4
In Activity 12.6, why are iron filings sprinkled?
💡 Hint:
The pattern appears after the cardboard is tapped.
Explanation:
The iron filings settle in the pattern of the field lines.
5
Why does the field at the centre of a circular coil add in one direction?
Model answer (board format)
The field of every small piece of the wire looks like a straight line at the centre. By the right-hand rule these lines point the same way inside the loop, so they add. With n turns the sum becomes n times as large.
Check your answer:
The solenoid and the electromagnet
परिनालिका और विद्युत चुंबक · NCERT 12.2.4 · solenoid
A coil wound as a cylinderNotes
Many circular turns of insulated copper wire, wrapped closely in the shape of a cylinder, make a solenoid. When a current flows, one end becomes a north pole and the other a south pole. The pattern is like a bar magnet.
Inside, the field lines are parallel straight lines. That means the field is the same at every point inside, so the field is uniform.
A soft-iron core
Place a magnetic material such as soft iron inside the solenoid and the strong field magnetises it. That magnet is called an electromagnet. Soft iron works as a magnet while the current is on. The figure in the book also shows a steel rod being magnetised by the same coil.
Worked exampleExample
Question: What is the field inside a long solenoid — zero, decreasing toward the end, or the same at every point?
Answer: The same at every point. The evidence is that the lines inside are parallel and straight. It is not zero, and in the ideal long solenoid it is not taken as decreasing toward the end.
10-second revision
- A solenoid is an insulated copper coil wound as a cylinder
- The field inside is uniform
- A solenoid with a soft-iron core is an electromagnet
Board tip · BSEBBoard tip
In the four-option item the answer is “the same at every point”. Do not pick “zero”.
Board tip · CBSEBoard tip
The difference between an electromagnet and a permanent magnet, in one line: when the current stops, soft iron is nearly ordinary again.
Check your understandingall correct = mastery ★
1
What is the magnetic field inside a long solenoid like?
💡 Hint:
Inside, the lines are parallel and straight.
Explanation:
The field inside is uniform, the same at every point.
2
One end of a current-carrying solenoid becomes a north pole and the other a south pole.
Explanation:
True — the pattern of the field is like a bar magnet.
3
The magnet made by placing soft iron inside a solenoid is called an ______.
💡 Hint:
A magnet made by the magnetic effect of a current.
Explanation:
It is called an electromagnet.
4
Define a solenoid and say why the field inside is called uniform.
Model answer (board format)
A solenoid is many closely wrapped circular turns of insulated copper wire in the shape of a cylinder. Inside, the field lines are parallel straight lines, so the field is the same at every point, that is, uniform. One end becomes a north pole and the other a south pole.
Check your answer:
Force on a conductor — Activity 12.7
चालक पर बल — क्रियाकलाप 12.7 · NCERT 12.3 · Activity 12.7 · Fleming left hand
The magnet exerts a force on the conductor tooNotes
A wire with current exerts a force on a nearby magnet. André Marie Ampère said the magnet must also exert an equal and opposite force on the current-carrying conductor.
The direction of the force depends on both the current and the field. The force is largest when the current and the field are perpendicular. Then the force is perpendicular to both.
Activity 12.7 — the aluminium rod shiftsActivity
Suspend a small aluminium rod AB, about 5 cm, horizontally from a stand with two wires. Place a horse-shoe magnet so the field is upward: north pole below the rod and south pole above. Connect the rod in series with a battery, a key and a rheostat.
Pass current from B to A. The rod shifts to the left. Reverse the current and the shift is to the right. Interchange the poles so the field is downward and the force reverses again.
Increase the current, use a stronger magnet, or use a longer rod — in all three the displacement increases.
Fleming left hand
Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. The forefinger is the field, the middle finger is the current. The thumb then gives the force or the motion.
Motors, generators, loudspeakers, microphones and many measuring instruments use current-carrying conductors and magnetic fields.
Worked exampleExample
Question: A wire carries current toward the east and the magnetic field is vertically downward. Which way is the force?
Answer: Open the left hand. Point the middle finger east (current) and the forefinger down (field). The thumb opens toward the north. The force is toward the north. Make the current west and the force becomes south.
If a proton moves freely in a magnetic field, its mass and its speed do not change. The direction of the velocity changes, so velocity and momentum can change. When the rule is used for an electron, take the current opposite to the motion of the electron.
10-second revision
- The force is perpendicular to both current and field
- Forefinger field, middle finger current, thumb force — left hand
- A larger current, a stronger magnet or a longer rod increases the displacement
Board tip · BSEBBoard tip
The left hand is for the force. The right hand is not the answer to this question.
Board tip · CBSEBoard tip
If an alpha particle going west is deflected north, the field is upward. The motion of a positive charge is the direction of the current.
Check your understandingall correct = mastery ★
1
When is the force on a current-carrying conductor the largest?
💡 Hint:
The three directions are mutually perpendicular.
Explanation:
The force is largest when the current is perpendicular to the magnetic field.
2
In Activity 12.7 the direction of the rod shift reverses when the current is reversed.
Explanation:
True — with current from B to A the rod goes left, and after the current is reversed it goes right.
3
In Fleming left hand, what does the thumb show?
💡 Hint:
The forefinger is the field, the middle finger is the current.
Explanation:
The thumb shows the force or the motion. Induced current belongs to the middle finger of the right hand.
4
The field that deflects an alpha particle going west toward the north points ______.
💡 Hint:
The motion of the positive charge is the current. Middle finger west, thumb north.
Explanation:
The field is vertically upward.
5
Which properties of a proton can change while it moves freely in a magnetic field, and which cannot?
Model answer (board format)
Velocity and momentum can change, because the force changes the direction. Mass does not change and speed does not change either, because this force is perpendicular to the motion.
Check your answer:
Electromagnetic induction and Fleming right hand
विद्युत चुंबकीय प्रेरण और फ्लेमिंग का दायाँ हाथ · Induced current · the rule in exercise item (iii)
A turning coil can have an induced currentNotes
When a conductor moves in a magnetic field, or the field linked with a coil changes, an emf and a current can appear in the conductor. This is electromagnetic induction.
The exercise asks which rule gives the direction of the current induced in a coil rotating in a magnetic field. That rule is Fleming right hand. A generator works on this idea: a coil rotates in a field and a current is induced.
| Rule | Hand | Fingers |
|---|---|---|
| Thumb rule | Right | Thumb current, fingers field |
| Fleming force | Left | Forefinger field, middle current, thumb force |
| Fleming induction | Right | Forefinger field, thumb motion, middle induced current |
The right hand is only for the induced current
Keep the three fingers of the right hand perpendicular. Forefinger for the field, thumb for the motion of the conductor, middle finger for the induced current. Do not mix this with the force from the left hand. The thumb rule is also a right hand, but it is for the field of a straight wire, not for an induced current.
Worked exampleExample
Question: A conductor is moving east and the field is upward. How do you find the direction of the induced current?
Answer: Use the right hand. Forefinger up (field), thumb east (motion). The direction the middle finger shows is the induced current. For this pair the middle finger points south, so the induced current is toward the south. If the force had been asked, the left hand would be used.
10-second revision
- Induction: a changing field or a moving conductor can produce a current
- Right hand: forefinger field, thumb motion, middle finger induced current
- Left hand is force, right hand is induced current
Board tip · BSEBBoard tip
Learn the table of three rules together. Papers often ask all three in one question.
Board tip · CBSEBoard tip
Write the generator when the question is an induced current from a rotating coil. The motor is the device of the force.
Check your understandingall correct = mastery ★
1
Which rule gives the induced current in a coil rotating in a magnetic field?
💡 Hint:
The thumb is the motion of the conductor.
Explanation:
Fleming right hand gives the direction of the induced current.
2
Fleming left hand gives the direction of the induced current.
Explanation:
False — the left hand gives the force. Induced current is the right hand.
3
In Fleming right hand the middle finger shows the direction of the ______.
💡 Hint:
The thumb is motion, the forefinger is the field.
Explanation:
The middle finger shows the induced current.
4
What is the basic idea in a generator?
💡 Hint:
The book lists the generator among devices that use a field and a conductor.
Explanation:
In a generator a coil rotates in a magnetic field and a current is induced.
5
Write the three direction rules: the field of a straight wire, the force on a conductor in a perpendicular field, and the induced current in a rotating coil.
Model answer (board format)
The field of a straight wire comes from the right-hand thumb rule: thumb current, fingers field. The force comes from Fleming left hand: forefinger field, middle finger current, thumb force. The induced current comes from Fleming right hand: forefinger field, thumb motion, middle finger induced current.
Check your answer:
The domestic circuit, the fuse and AC–DC
घरेलू परिपथ, फ्यूज और AC–DC · NCERT 12.4 · 220 V · 50 Hz
Three wires and two circuitsNotes
Power reaches a house from poles or underground cables. The wire with red insulation is live and the black wire is neutral. In our country the potential difference between them is 220 V. This supply is alternating (AC) with frequency 50 Hz, so the direction reverses every cycle and one cycle takes 1/50 of a second. The current of a cell is direct (DC) and flows one way.
On the meter board the main fuse comes first and then the main switch. Often there are two circuits: heavy appliances such as a geyser and a cooler on 15 A, bulbs and fans on 5 A. Appliances are connected in parallel between live and neutral, so each gets the same potential difference. Each appliance has its own switch.
The green wire and the fuseCaution
The green earth wire is connected to a metal plate buried in the earth near the house. The metal body of a press, toaster, fan or fridge is joined to it. Leaking current gets a low-resistance path to the earth, the potential of the body stays equal to the earth, and the user does not get a severe shock.
A fuse protects the circuit from overloading or a short circuit. Joule heating melts the fuse and breaks the circuit. In a short circuit the red and black wires meet directly, when the insulation is damaged or the appliance is faulty, and the current rises suddenly. Overloading also happens if too many appliances are put on one socket, or if the supply voltage jumps.
| Wire | Colour | Job |
|---|---|---|
| Live | Red | Supply |
| Neutral | Black | Return |
| Earth | Green | Safe path for a leak |
Worked example — a 2 kW ovenExample
Question: A 2 kW oven is run on a 220 V domestic circuit whose current rating is 5 A. What happens?
Formula: P = VI, so I = P / V.
Substitute: P = 2 kW = 2000 W, V = 220 V.
I = 2000 / 220 = 100/11 = 9.09 A, about 9.1 A.
9.1 A is above the 5 A rating. The fuse melts and the circuit opens. An oven of this size belongs on the 15 A circuit, not on the 5 A circuit of bulbs and fans.
10-second revision
- AC 220 V, 50 Hz; red live, black neutral, green earth
- Appliances in parallel; 15 A for heavy appliances, 5 A for bulbs and fans
- The fuse melts by Joule heating; in a short circuit the current rises suddenly
Board tip · BSEBBoard tip
The green wire is not live. That slip often traps people in an objective item.
Board tip · CBSEBoard tip
In the oven number item write I = P/V, substitute watts and volts, and compare the answer with 5 A.
Check your understandingall correct = mastery ★
1
In a domestic supply the wire with green insulation is —
💡 Hint:
Red is live, black is neutral.
Explanation:
The green wire is the earth. It is not live.
2
At the time of a short circuit the current in the circuit rises heavily.
Explanation:
True — when live and neutral meet directly the current rises suddenly.
3
The AC supply in homes in India is ______ V and 50 Hz.
💡 Hint:
Between live and neutral.
Explanation:
The potential difference is 220 V and the frequency is 50 Hz.
4
About how much current does a 2 kW oven draw at 220 V?
💡 Hint:
I = P/V and write P in watts.
Explanation:
I = 2000/220 = 9.09 A, about 9.1 A. That is above the 5 A rating.
5
Write the job of the earth wire and say why a metal-bodied appliance is earthed.
Model answer (board format)
The green wire is joined to a metal plate buried in the earth. The metal body of the appliance is connected to it, so that leaked current has a low-resistance path to the earth. The potential of the body stays equal to the earth and the user does not get a severe shock.
Check your answer:
❓ Full question bank — with answers and explanations — 71 questions
Pick a type. The 39 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual70 tried · 0 correctMultiple choiceMCQ160 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason50 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA130 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
Multiple choice
0/16Pick one option. A wrong try brings a hint.
1
The field near a long straight current-carrying wire is —
💡 Hint:
Iron filings settle in circles.
Explanation:
The field is concentric circles.
2
At a short circuit the current —
💡 Hint:
Live and neutral meet directly.
Explanation:
The current rises suddenly and heavily.
3
In the right-hand thumb rule the fingers show —
💡 Hint:
The thumb is the current.
Explanation:
The fingers curl along the field lines.
4
Inside a long solenoid the field —
💡 Hint:
The lines are parallel.
Explanation:
The field inside is uniform.
5
In Fleming left hand the forefinger shows —
💡 Hint:
Middle finger current, thumb force.
Explanation:
The forefinger shows the magnetic field.
6
The colour of the earth wire is —
💡 Hint:
Red is live.
Explanation:
Green is earth.
7
The frequency of the home supply is —
💡 Hint:
The volt value is 220, the hertz value is different.
Explanation:
The frequency is 50 Hz.
8
The fuse wire melts because of —
💡 Hint:
The heating from Chapter 11.
Explanation:
Joule heating melts the fuse when the current is too large.
9
Two field lines —
💡 Hint:
The needle shows one direction.
Explanation:
Two lines do not cross.
10
The force is maximum when current and field are —
💡 Hint:
The three directions are perpendicular.
Explanation:
The force is largest in the perpendicular case.
11
The core of an electromagnet is usually —
💡 Hint:
Inside the solenoid.
Explanation:
Soft iron becomes the core of an electromagnet.
12
How are appliances connected between live and neutral?
💡 Hint:
Each one needs the same potential difference.
Explanation:
Appliances are connected in parallel.
13
The field of a current coming out of the page is —
💡 Hint:
Thumb toward you.
Explanation:
A current out of the page has an anticlockwise field.
14
The 15 A circuit is for which appliances?
💡 Hint:
5 A is for bulbs and fans.
Explanation:
Heavy appliances go on the 15 A circuit.
15
The field lines around a straight current-carrying wire are —
💡 Hint:
Activities 12.1 and 12.4.
Explanation:
The field lines are circles centred on the wire. The direction comes from the thumb rule.
16
Fleming’s left-hand rule gives —
💡 Hint:
Thumb force, forefinger field, middle finger current.
Explanation:
The left hand gives the force. The right hand gives the induced current.
True or false
0/81
A wire with green insulation is usually the live wire.
Explanation:
False — green is earth. Red is live.
2
The field at the centre of a long circular coil is parallel straight lines.
Explanation:
True — at the centre the arcs look straight, and in a long coil they are parallel.
3
Inside a magnet the field lines go from north to south.
Explanation:
False — inside, the direction is from south to north. Outside it is from north to south.
4
Fleming right hand gives the force on a straight wire.
Explanation:
False — force is the left hand. The right hand is the induced current.
5
Homes in India receive 220 V, 50 Hz AC.
Explanation:
True — the direction reverses every cycle.
6
The neutral wire has red insulation.
Explanation:
False — neutral is black. Red is live.
7
Increasing the current increases the field of a straight wire at a point.
Explanation:
True — the deflection of the needle increases too.
8
Field lines have open ends; they are not closed curves.
Explanation:
False — outside N to S and inside S to N together make closed curves.
Fill in the blanks
0/81
The thumb of the right hand is pointed along the ______.
💡 Hint:
The thumb points along the current.
Explanation:
The fingers are the field.
2
The colour of the earth wire is ______.
💡 Hint:
Green.
Explanation:
Not red.
3
The potential difference between live and neutral is ______ volt.
💡 Hint:
220 V.
Explanation:
The frequency 50 Hz is a different number.
4
The thumb of Fleming left hand gives the direction of the ______.
💡 Hint:
The thumb gives the force or the motion.
Explanation:
The forefinger is the field.
5
The frequency of the AC supply is ______ hertz.
💡 Hint:
50 Hz.
Explanation:
Not the volt number.
6
A fuse melts because of ______ heating.
💡 Hint:
Joule heating.
Explanation:
The I²R heat.
7
Outside a magnet the field lines go from the ______ pole to the south pole.
💡 Hint:
From the north pole.
Explanation:
The direction of a free north pole.
8
A solenoid with a soft-iron core is an ______.
💡 Hint:
An electromagnet.
Explanation:
Soft iron nearly lets go when the current stops.
Match
0/21
Match the wire or circuit with its job.
Column B: A. Neutral · B. Earth · C. A heavy appliance such as a geyser · D. Live
1. Red wire
2. Black wire
3. Green wire
4. 15 A circuit
Explanation:
Red is live, black is neutral, green is earth, 15 A is for heavy appliances.
2
Match the rule with its job.
Column B: A. Field of a straight wire · B. Force on a conductor · C. Induced current · D. Shape of a field line
1. Right-hand thumb
2. Fleming left
3. Fleming right
4. Closed curve
Explanation:
Thumb for the field, left hand for the force, right hand for the induced current, and the line is a closed curve.
Assertion–reason
0/5Check both statements, then see whether the reason explains the assertion.
1
Assertion (A): A compass turns near a wire that carries current.
Reason (R): An electric current produces a magnetic field.
Explanation:
Both are true and R correctly explains A.
2
Assertion (A): Two magnetic field lines do not cross.
Reason (R): At a crossing a compass would have to show two directions at once.
Explanation:
Both are true and R is the correct reason.
3
Assertion (A): A fuse protects a circuit from overloading.
Reason (R): A fuse increases the current further.
Explanation:
A is true. R is false — the fuse melts and stops the current.
4
Assertion (A): The home supply is 50 Hz AC.
Reason (R): The green wire is the live wire.
Explanation:
A is true. R is false — the green wire is earth, not live.
5
Assertion (A): The field inside a solenoid is zero.
Reason (R): Parallel field lines inside mean the field is the same at every point.
Explanation:
A is false. R is true — the field is not zero, it is uniform.
Coefficient practice
0/4These equations are not results of this chapter. They are only practice in filling coefficients.
1
This tray is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
2
This tray is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
N2 + H2 → NH3
Explanation: N2 + 3H2 → 2NH3
3
This tray is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
Na + Cl2 → NaCl
Explanation: 2Na + Cl2 → 2NaCl
4
This tray is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
Fe + O2 → Fe2O3
Explanation: 4Fe + 3O2 → 2Fe2O3
Classify
0/21
Place each job with the right rule.
Field of a straight wire
Force on a conductor
Induced current
Curl for current out of the page
Explanation:
Field from the thumb rule, force from the left hand, induced current from the right hand.
2
Place each fact as AC mains or DC from a cell.
50 Hz
Direction reversing again and again
Current in one direction only
220 V between live and neutral
Explanation:
The mains is AC, 220 V and 50 Hz. A cell gives DC.
Very short answer
0/51
Define a magnetic field in one line.
Model answer (board format)
The region around a magnet in which its force can be detected is called a magnetic field.
Check your answer:
2
Write the right-hand thumb rule.
Model answer (board format)
Hold a straight current-carrying wire in the right hand so that the thumb points along the current. The fingers curl in the direction of the field lines.
Check your answer:
3
Write two safety measures common in domestic circuits.
Model answer (board format)
The fuse and earthing. The fuse melts on too much current. The green wire joins a metal body to the earth.
Check your answer:
4
When does a short circuit occur?
Model answer (board format)
When the live and neutral wires come into direct contact. This happens if the insulation is damaged or the appliance is faulty, and the current rises suddenly.
Check your answer:
5
What is an electromagnet?
Model answer (board format)
An electromagnet is the magnet made by placing a core such as soft iron inside a current-carrying solenoid.
Check your answer:
Short answer
0/41
Write three properties of magnetic field lines.
Model answer (board format)
Outside they go from north to south and inside from south to north, so they are closed curves. Crowded lines show a stronger field. Two lines do not cross.
Check your answer:
2
In Activity 12.7, when will the displacement of the rod increase? Write three points.
Model answer (board format)
The displacement increases if the current in the rod is increased, if a stronger horse-shoe magnet is used, and if the length of the rod is increased.
Check your answer:
3
A 1 kW heater runs at 220 V. Find the current and say whether it suits a 5 A circuit.
Model answer (board format)
I = P/V = 1000 W / 220 V = 4.55 A. 4.55 A is below 5 A, so it can run on a 5 A circuit. A 2 kW oven draws 9.1 A and should not run on a 5 A circuit.
Check your answer:
4
Write two causes of overloading and one precaution to avoid it.
Model answer (board format)
Connecting too many appliances to one socket, or a sudden rise in the supply voltage. Precaution: do not put too many appliances on one socket, and fit a fuse of the right current rating.
Check your answer:
Long answer
0/41
Compare the fields of a straight wire, a circular coil and a solenoid. Also write the rule used to find the direction.
Model answer (board format)
The field of a straight wire is concentric circles. It grows if the current increases and falls if the distance increases. At the centre of a circular coil the lines are nearly straight, and with n turns the field is n times as large. A solenoid is like a bar magnet; inside, the lines are parallel and the field is uniform. The direction comes from the right-hand thumb rule.
Check your answer:
2
Write both of Fleming rules. In one sentence say which rule belongs to a motor and which to a generator.
Model answer (board format)
Left hand: forefinger field, middle finger current, thumb force. Right hand: forefinger field, thumb motion of the conductor, middle finger induced current. A motor uses the force, so the left hand; in a generator a coil rotates and a current is induced, so the right hand.
Check your answer:
3
Describe a domestic circuit in words. Write why a fuse and an earth wire are needed, with an example.
Model answer (board format)
The red live and black neutral pass through the main fuse into the meter and then to the main switch. A 15 A circuit takes appliances such as a geyser and a 5 A circuit takes bulbs and fans. Appliances are in parallel. The fuse melts by Joule heating and stops too large a current, such as a 2 kW oven on a 5 A circuit drawing about 9 A. The green wire joins a metal body to the earth so that a leak does not shock the user.
Check your answer:
4
Why are a fuse and earthing used in a household circuit? Also write where each is placed.
Model answer (board format)
The fuse is in series and melts to open the circuit when the current is too large. The earth wire is joined to the metal case so that a leakage current goes into the ground and does not shock a person. The fuse is in the live line; the earth wire is on the case.
Check your answer:
BSEB model paper · practice
0/7This model set is for practice. It is not a question from any year’s annual examination. Annual questions will be added only when a source page is available.
1
Which of the following gives the direction of an induced current?
💡 Hint:
The thumb is the motion.
Explanation:
Fleming right hand gives the induced current.
2
One cause of overloading is —
💡 Hint:
A load above the current rating.
Explanation:
Too many appliances on one socket can overload it.
3
The colour of the live wire is ______.
💡 Hint:
Red.
Explanation:
Black is neutral.
4
Why is soft iron used as the core of a solenoid?
Model answer (board format)
The strong field of the solenoid magnetises the soft iron. While the current flows it works as an electromagnet.
Check your answer:
5
This tray is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
C + O2 → CO2
Explanation: C + O2 → CO2
6
Write the right-hand thumb rule, Fleming left hand and Fleming right hand. Also write one use of each.
Model answer (board format)
Thumb rule: thumb current, fingers field. Use: direction of the field of a straight wire or a loop. Left hand: forefinger field, middle finger current, thumb force. Use: the force on a conductor in a motor. Right hand: forefinger field, thumb motion, middle finger induced current. Use: the current in a coil rotating in a generator.
Check your answer:
7
To make an electromagnet the wire is wound as —
💡 Hint:
The use that follows Activity 12.5.
Explanation:
Wire wound on a soft-iron core makes an electromagnet. The magnetism nearly goes when the current stops.
CBSE-style questions
0/6These are competency-based practice questions. They are not copies of a CBSE paper.
1
A student runs a 2 kW oven on a 220 V, 5 A circuit. The most likely result is —
💡 Hint:
I = P/V.
Explanation:
I = 2000/220 ≈ 9.1 A, which is above 5 A, so the fuse melts.
2
A loop on a table has a current that is anticlockwise as seen from above. The field inside the loop is —
💡 Hint:
Fingers anticlockwise, thumb up.
Explanation:
For an anticlockwise current the field inside is upward. For clockwise it is downward.
3
Assertion (A): A fridge with a metal body should be earthed.
Reason (R): The green wire takes leaked current to the earth along a low-resistance path.
Explanation:
Both are true and R is the correct reason.
4
Assertion (A): When Fleming left hand is used for an electron, the current direction must be taken with care.
Reason (R): The direction of current is taken as the same as the motion of the electron.
Explanation:
A is true. R is false — current is taken opposite to the motion of the electron.
5
A horizontal wire carries current from east to west. Using the right hand, say how the field turns when viewed from the east end.
Model answer (board format)
The thumb points west. Viewed from the east end, that is along the current, the field turns clockwise in a plane perpendicular to the wire. Viewed from the west end the same field looks anticlockwise.
Check your answer:
6
A cooler is rated 1500 W and runs at 220 V. Find the current. Should it run on the 5 A circuit or the 15 A circuit? Write the reason.
Model answer (board format)
I = P/V = 1500/220 = 6.82 A. This is above 5 A and below 15 A, so the cooler should run on the 15 A circuit. On the 5 A circuit the fuse can melt.
Check your answer:
🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
Switch board with BSEB | CBSE above. The lessons follow the same NCERT chapter.
BSEB model · practiceBoard tip
This page has no verified annual-exam question, because no source page has been added. The model set below is practice in the board pattern.
🏛️ Model questions on one page →
The verified label will be used only when a source page for the question is available.
CBSE-style · competency-based
These are case and assertion-reason practice items. Do not treat them as past CBSE questions.
🔁 Spaced review — today’s questions
Wrong questions return soon; correct ones return after a few days.
🧠 What you learned + equation sheet
What you learned
- A wire with current behaves like a magnet; the compass needle turns.
- Field lines go from north to south outside, from south to north inside, and never cross.
- In the right hand the thumb is the current and the fingers are the direction of the field.
- The field of a solenoid is like a bar magnet; inside, the lines are parallel and the field is uniform.
- The force is largest when current and field are perpendicular; the direction comes from Fleming left hand.
- Homes get 220 V, 50 Hz AC; the fuse and the green earth wire are there for safety.
| What | Keep this |
|---|---|
| Right-hand thumb | thumb = current, fingers = field |
| Fleming left | forefinger field, middle finger current, thumb force |
| Fleming right | forefinger field, thumb motion, middle finger induced current |
| Inside a solenoid | parallel lines, same field at every point |
| Mains | 220 V, 50 Hz, AC |
| Wire colours | live red, neutral black, earth green |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.