Class 10 Science · Chapter 12

Magnetic Effects of Electric Current

279 Class 10 Science questions on Magnetic Effects of Electric Current from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

NCERT exercises

Exercises (9) Intext Questions (Page 196) (1) Intext Questions (Page 200) (3) Intext Questions (Page 201) (3) Intext Questions (Page 203) (3) Intext Questions (Page 205) (3)

NCERT Exemplar exercises

Multiple Choice Questions (12) Short Answer Questions (12) Long Answer Questions (8)

CBSE Class 10 Science previous year papers, with answers →

Questions · page 13 of 14

Q241 CBSE 2020
At the time of short circuit, the electric current in the circuit :
1. (a)vary continuously
2. (b)does not change
3. (c)reduces substantially
4. (d)increases heavily
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(d) increases heavily

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Q242 CBSE 2020
Two coils of insulated copper wire are wound over a non-conducting cylinder as shown. Coil 1 has comparative large number of turns. State your observations, when
1. (i)Key K is closed.
2. (ii)Key K is opened. Give reason for each of your observations.
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Closing K deflects G briefly, opening K deflects it oppositely, because the changing field of coil 1 induces a current in coil 2.
(i) When key K is closed, the galvanometer G shows a deflection for a very short time (a momentary deflection), and its needle then returns to zero. (ii) When key K is opened, G again shows a momentary deflection, but in the direction opposite to that in (i), and then returns to zero. Reason: on closing or opening the key, the current in coil 1 changes (it rises from zero, or falls to zero), so the magnetic field of coil 1 passing through coil 2 changes. This changing magnetic field induces a current in coil 2 (electromagnetic induction), which deflects G. The field increases in (i) and decreases in (ii), so the induced currents are in opposite directions; while the current in coil 1 is steady, the field does not change and no current is induced.

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Q243 CBSE 2020
Give reasons for the following :
1. (i)There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
2. (ii)The current carrying solenoid when suspended freely rests along a particular direction.
3. (iii)The burnt out fuse should be replaced by another fuse of identical rating.
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The ends act as poles; a free solenoid rests north-south like a bar magnet; only a fuse of identical rating protects the circuit.
(i) A current-carrying solenoid behaves like a bar magnet, its two ends acting as the north and south poles. The magnetic field is strong near these poles (ends), where the field lines are crowded: the lines, parallel inside the solenoid, spread out (diverge) as they come out of the north-pole end and come together (converge) as they go into the south-pole end, each forming a closed loop. (ii) A current-carrying solenoid behaves like a bar magnet, so when it is suspended freely the Earth's magnetic field turns it, like a compass needle, until it rests along the north-south direction. (iii) A fuse of higher rating would not melt even when a current greater than the safe limit flows, so the wiring and appliances would be damaged; a fuse of lower rating would melt even with the normal current. A fuse of identical rating melts just when the current exceeds the safe limit, so it protects the circuit.

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Q244 CBSE 2020
(a) A coil of insulated wire is connected to a galvanometer. What would be observed if a strong bar magnet with its south pole towards one face of the coil is
1. (i)moved quickly toward it ?
2. (ii)moved quickly away from it ?
3. (iii)held stationary near it ? (b) Name the phenomena involved. (c) State the conclusion based on the observations in (i), (ii) and (iii).
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Moving the magnet towards or away from the coil deflects the galvanometer in opposite directions; a stationary magnet gives none. This is electromagnetic induction.
(a) (i) The galvanometer needle shows a momentary deflection to one side (say, to the left). (ii) The needle again shows a momentary deflection, but in the opposite direction (to the right). (iii) No deflection: the needle stays at zero. (b) Electromagnetic induction. (c) Motion of a magnet with respect to the coil (a change in the magnetic field around the coil) induces an electric current in the coil. The current lasts only as long as the motion continues, and its direction reverses when the direction of motion is reversed.

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Q245 CBSE 2020

What is a solenoid ? What does the magnetic field pattern inside the solenoid indicate ? State how this field can be utilised to make an electromagnet.

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A solenoid is a closely wound coil of insulated copper wire; its field is uniform inside, and a soft-iron core inside makes an electromagnet.
A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Inside a current-carrying solenoid the field lines are parallel straight lines, so the magnetic field is the same at all points inside it: the field inside the solenoid is uniform. (Outside, its field is like that of a bar magnet, with a north pole at one end and a south pole at the other.) This strong field can be used to magnetise a piece of magnetic material, such as soft iron, placed inside the coil. The soft-iron core becomes a magnet while the current flows, and the magnet so formed is called an electromagnet.

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Q246 CBSE 2020
1. (a)Draw the pattern of magnetic field lines due to a magnetic field through and around a current carrying circular loop.
2. (b)Name and state the rule to find out the direction of magnetic field inside and around the loop.
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Field lines are concentric circles near the wire, straight and parallel at the loop's centre; the right-hand thumb rule gives their direction.
(a) The pattern is shown in the figure. Near each point where the loop crosses the paper, the field lines are concentric circles around the wire; they grow larger towards the centre of the loop, and at the centre they are straight lines parallel to the axis of the loop, all pointing the same way. Field lines never cross, and the field inside the loop is stronger than outside. (b) Right-hand thumb rule: imagine holding the current-carrying conductor in the right hand with the thumb pointing in the direction of the current; the fingers then wrap around the conductor in the direction of the magnetic field lines. Applied to every part of the loop, it gives the direction of the field inside and around the loop.

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Q247 CBSE 2020
Study the diagram given below and answer the questions that follow :
1. (a)Why do the iron filings arrange in such a pattern ?
2. (b)What does this pattern demonstrate ?
3. (c)Why do the iron filings near the bar magnet seem to align in the shape of closed curves ?
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Filings align along the magnet's field lines, which are closed curves; they crowd near the poles where the field is strongest.
(a) The bar magnet exerts a magnetic force in the region around it. Each iron filing in this region is magnetised, becomes a tiny magnet, and is turned by this force to lie along the direction of the magnetic field at its position, so the filings arrange themselves along definite curved lines. (b) The pattern demonstrates the magnetic field around the magnet, the region in which its force can be detected. The lines along which the filings align are the magnetic field lines, and the crowding of filings near the poles shows that the field is strongest there. (c) Magnetic field lines are closed curves: outside the magnet they run from the north pole to the south pole, and inside the magnet from the south pole back to the north pole. The filings align along these lines, so near the magnet they appear as closed curves running from one pole to the other.

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Q248 CBSE 2020

What is a solenoid ? Draw the pattern of magnetic field lines due to a current carrying solenoid. What does the field pattern inside the solenoid indicate ? State one use of this field.

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A solenoid is a closely wound coil; its field is like a bar magnet's, uniform inside, and it is used to make an electromagnet.
Solenoid: a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Field lines (see the figure): the pattern is that of a bar magnet. Inside the coil the lines are straight, parallel and equally spaced, running from the S end to the N end; outside they leave the N end, curve round and enter the S end. Every line is a closed loop and no two lines cross. Inside: the parallel, equally spaced lines indicate that the magnetic field is the same at all points inside the solenoid, that is, the field is uniform. Use: the strong field inside can magnetise a piece of magnetic material such as soft iron placed in the coil, making an electromagnet.

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Q249 CBSE 2020

What is overloading and short circuiting ? State the function of earth wire in a domestic circuit.

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Overloading is excess current from too many appliances; short circuit is live–neutral contact; the earth wire protects the user from shock.
Overloading: the appliances connected to a circuit draw more current than it is designed to carry. It is caused by connecting too many appliances to a single socket, or by an accidental hike in the supply voltage, and the excess current overheats the wires. Short-circuiting: the live wire and the neutral wire come into direct contact (for example, when the insulation is damaged or an appliance is faulty). The resistance of the circuit becomes very small, so the current in the circuit abruptly increases to a very large value. Earth wire: it connects the metallic body of an appliance to a metal plate buried deep in the earth and provides a low-resistance conducting path for the current. Any current that leaks to the metal body flows to the earth, so the body stays at the potential of the earth and the user does not get a severe electric shock.

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Q250 CBSE 2020
1. (a)What is an electromagnet ? List any two uses.
2. (b)Draw a labelled diagram to show how an electromagnet is made.
3. (c)State the purpose of soft iron core used in making an electromagnet.
4. (d)List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.
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An electromagnet is a soft iron core magnetised by current in a coil; more current or more turns make it stronger.
(a) An electromagnet is a temporary magnet made by placing a soft iron core inside a solenoid (a coil of many turns of insulated copper wire); when a current flows through the coil, the soft iron core is magnetised and behaves like a magnet as long as the current flows. Uses (any two): electric bells, electric motors, cranes that lift heavy iron loads, relays. (b) Labelled diagram: a coil of insulated copper wire wound on a soft iron core and connected to a battery through a key, with arrows showing the direction of the current (see the figure). (c) The soft iron core increases the strength of the electromagnet, and because it is soft iron it loses its magnetism when the current is switched off. (d) (i) By increasing the current through the coil; (ii) by increasing the number of turns in the coil.

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Q251 CBSE 2020
1. (a)Explain with the help of the pattern of magnetic field lines the distribution of magnetic field due to a current carrying a circular loop.
2. (b)Why is it that the magnetic field of a current carrying coil having $n$ turns, is ‘ $n$ ’ times as large as that produced by a single turn (loop) ?
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Near a loop's wire the lines are circles, straight at the centre; $n$ turns add their fields, so the coil's field is $n$ times.
(a) Near every part of the loop the field lines are concentric circles, as round a straight conductor, and these circles become larger and larger as we move away from the wire, showing that the field weakens with distance from the wire. By the right-hand thumb rule every part of the loop sends its field through the loop in the same direction, so inside the loop the fields add. At the centre of the loop the arcs of these big circles appear as straight, parallel lines along the axis: the field there is nearly uniform and perpendicular to the plane of the loop. Outside the loop the lines curve back, so each line is a closed curve round the wire. (b) The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it. In a coil of $n$ turns the same current flows through every turn in the same direction, so each turn produces the same field at the centre, pointing the same way, and the fields due to the $n$ turns just add up: $B_{coil} = n B_{1}$ , $n$ times the field of a single turn.

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Q252 CBSE 2020
1. (a)State Fleming’s Left-hand rule.
2. (b)List three characteristic features of the electric current used in our homes.
3. (c)What is a fuse ? Why is it called a safety device ?
4. (d)Why is it necessary to earth metallic electric appliances ?
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Fleming's left-hand rule; household a.c. at 50 Hz and 220 V; a fuse melts to break an overloaded circuit; earthing prevents shock.
(a) Fleming’s left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the motion of the conductor, that is, of the force acting on it. (b) The current used in our homes is alternating current, which reverses its direction periodically; its frequency is $50$ Hz; and the potential difference between the live wire and the neutral wire is about $220$ V. (c) A fuse is a safety device: a short piece of wire of low melting point connected in series in the live wire of a circuit or appliance. It is called a safety device because, when an unduly high current flows through it because of overloading or short-circuiting, the heat produced ( $H = I^{2} R t$ ) melts the fuse wire and breaks the circuit, stopping the current and preventing damage to the circuit and the appliances. (d) Earthing joins the metallic body of the appliance to the earth through a low-resistance conducting path. If current leaks to the body, it flows to the earth through this path and the body stays at the earth's potential, so the user is protected from a severe electric shock.

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Q253 CBSE 2020
1. (a)State with reasons the mode of connecting all electrical appliances in common domestic electric circuits.
2. (b)Which two separate circuits are often used in domestic electric circuits and why ?
3. (c)When does an electric short circuit occur ? How can it be prevented ?
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Appliances are in parallel, with separate 15 A and 5 A circuits; a short circuit (live touching neutral) is prevented by a fuse.
(a) Appliances are connected in parallel, because (any two): each gets the full mains voltage of $220$ V; each can be switched on or off independently; if one fails or is switched off, the others keep working. (b) A $15$ A circuit for appliances of high power rating, such as geysers and air coolers, and a $5$ A circuit for bulbs, fans and similar appliances, because appliances of different power ratings draw very different currents. (c) A short circuit occurs when the live and neutral wires come into direct contact, for example through damaged insulation or a faulty appliance, so the current rises abruptly (overloading). It is prevented by a fuse of proper rating in the live wire and by good-quality, well-insulated wiring.

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Q254 CBSE 2020

“A current carrying straight conductor experiences a force perpendicular to its length and the magnetic field.” Design an activity for the verification of the above mentioned statement and describe it with a labelled diagram.

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A current-carrying rod in a magnetic field is pushed sideways, perpendicular to its length and the field; reversing either reverses the push.
Activity: hang a small aluminium rod AB (about $5$ cm long) horizontally from a stand by two connecting wires, so that it lies between the poles of a strong horseshoe magnet, with the north pole vertically below the rod and the south pole vertically above it; the field at the rod then points vertically upwards. Connect the rod in series with a battery, a plug key and a rheostat, as in the labelled diagram. Observation: when the key is inserted and a current flows from B to A, the rod is displaced sideways (to the left as seen from end A), horizontally, at right angles both to its own length and to the vertical field. When the current is reversed, the rod is displaced to the right; when the magnet is turned over, the displacement also reverses. Conclusion: a current-carrying straight conductor placed in a magnetic field experiences a force perpendicular to its length and to the field; its direction, given by Fleming's left-hand rule, depends on the directions of the current and of the field.

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Q255 CBSE 2019

What is the function of a galvanometer in a circuit ?

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A galvanometer detects the presence of an electric current in a circuit and shows its direction.
A galvanometer detects the presence of an electric current in a circuit and shows its direction: its pointer stays at the central zero when no current flows and deflects to one side or the other according to the direction of the current.

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Q256 CBSE 2019

Draw magnetic field lines around a bar magnet.

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Closed field lines leave the north pole and enter the south pole outside the magnet, crowded near the poles and never crossing.
Draw a bar magnet with its poles labelled N and S and closed field lines around it: the lines come out of the north pole, curve round the magnet and go into the south pole, with arrows from N to S outside the magnet (inside the magnet they run from S to N, so each line is a closed loop). The lines are crowded near the poles, where the field is strongest, spread out farther away, and no two lines cross each other.

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Q257 CBSE 2019

Draw magnetic field lines in and around a current carrying straight solenoid.

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Inside the solenoid the lines are parallel and equally spaced; outside they spread out like those of a bar magnet.
Draw the solenoid (a long coil of many turns) connected to a cell, with the direction of the current marked in its turns, and draw its field lines as follows: (i) Inside the solenoid, the field lines are parallel, straight and equally spaced along its axis: the field inside is uniform. (ii) Outside, the lines come out of one end, spread out, curve round and enter the other end, like the field lines of a bar magnet; each line is a closed curve and no two lines cross. (iii) Polarity: the end at which the current, seen from outside, flows anticlockwise is the north pole (N); the end at which it flows clockwise is the south pole (S). (iv) Direction: outside the solenoid the lines point from N to S; inside, from S to N.

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Q258 CBSE 2019
It is established that an electric current through a conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving
1. (i)alpha particles,
2. (ii)neutrons ? Justify your answer in each case.
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(i) Yes: a beam of charged alpha particles is a current; (ii) no: neutrons are uncharged, so there is no current and no field.
(i) Yes. Alpha particles are positively charged (each carries a charge of $+ 2 e$ ), so a beam of moving alpha particles is a flow of charge, that is, an electric current in the direction of the beam. Like any current, it produces a magnetic field around it. (ii) No. Neutrons carry no charge, so a beam of moving neutrons is not an electric current, and no magnetic field is produced around it.

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Q259 CBSE 2019
A compass needle is placed near a current carrying straight conductor. State your observation for the following cases and give reasons for the same in each case :
1. (a)Magnitude of electric current is increased.
2. (b)The compass needle is displaced away from the conductor.
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(a) The deflection increases because the field gets stronger; (b) it decreases because the field weakens with distance.
(a) The deflection of the compass needle increases, because the magnetic field produced by the conductor becomes stronger when the current through it is increased. (b) The deflection of the compass needle decreases, because the magnetic field of the conductor becomes weaker as the distance from the conductor increases.

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Q260 CBSE 2019

List four properties of magnetic field lines.

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Field lines run from north to south outside a magnet, are closed curves, are crowded where the field is strong, and never cross.
(1) Outside a magnet, magnetic field lines emerge from the north pole and merge at the south pole; inside the magnet they run from the south pole to the north pole. (2) Magnetic field lines are closed curves. (3) The field lines are crowded near the poles, where the magnetic field is stronger: the closer the lines, the stronger the field. (4) No two field lines ever cross (intersect) each other, because the field has only one direction at a point. Other correct properties, such as the tangent to a field line at any point giving the direction of the field there, also earn credit.

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