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 11 of 14

Q201 CBSE 2023

For the current carrying solenoid as shown, draw magnetic field lines and give reason to explain that out of the three points A, B and C, at which point the field strength is maximum and at which point it is minimum ?

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The field is strongest at A, inside the solenoid, and weakest at B, just outside its middle.
Field lines: inside the solenoid they are straight, parallel to the axis and equally spaced, showing a strong and uniform field; outside they come out of one end, spread far apart and return to the other end, so the solenoid acts like a bar magnet. The field strength is **maximum** at A, because A is inside the solenoid where the lines are closest together and the field is uniform and strongest. It is **minimum** at B, because B lies just outside the middle of the winding, where the returning field lines have spread over a very large region and are farthest apart; alongside the middle of a long solenoid the outside field is almost zero. The point C, which lies just beyond the end face, has a field between the two, because there the lines are converging in order to enter the solenoid and so are still fairly close together.

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Q202 CBSE 2023

Draw the pattern of the magnetic field produced around a vertical current carrying straight conductor passing through a horizontal cardboard. Mark the direction of current and the magnetic field lines. Name and state the rule which is used to determine the direction of magnetic field associated with a current carrying conductor.

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Field lines are concentric circles around the wire, crowded near it; the right-hand thumb rule gives their direction.
Pattern: the magnetic field lines around the vertical conductor are concentric circles centred on the wire and lying in the plane of the horizontal cardboard. They are crowded near the wire and become further apart as the distance from it grows, because the field weakens with distance. Mark an upward arrow on the wire for the current; the circles then carry arrowheads running anticlockwise when the cardboard is seen from above, and they reverse if the current is reversed. Rule: the right-hand thumb rule (Maxwell's corkscrew rule). Hold the conductor in your right hand with the thumb pointing in the direction of the current; the direction in which the fingers curl around the conductor gives the direction of the magnetic field lines.

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Q203 CBSE 2023

With the help of a labelled circuit diagram, illustrate the pattern of the magnetic field lines of the magnetic field produced around a straight current carrying conductor. Explain how, with the help of right-hand thumb rule, we can determine and mark the direction of magnetic field lines due to a current.

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Iron filings round a vertical wire form concentric circles, crowded near the wire; the right-hand thumb rule gives their direction.
The circuit consists of a straight thick copper wire passed vertically through the centre of a horizontal cardboard sheet and connected in series with a battery and a plug key. When iron filings are sprinkled on the cardboard, the key is closed and the cardboard is tapped gently, the filings settle into a pattern of concentric circles centred on the wire and lying in the plane of the cardboard, that is, in the plane perpendicular to the wire. The circles are crowded together near the wire and become farther apart as the distance from the wire increases, showing that the magnetic field is stronger close to the conductor and becomes weaker away from it. The direction of these field lines is given by the right-hand thumb rule: hold the current-carrying straight conductor in your right hand with the thumb pointing in the direction of the current; the fingers wrapped around the conductor then point in the direction of the magnetic field lines. So if the current flows out of the plane of the paper the field lines are marked anticlockwise, and if it flows into the paper they are marked clockwise. A small compass placed at any point on the cardboard confirms this, its needle setting itself along the tangent to the circle at that point and reversing when the current is reversed.

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Q204 CBSE 2023
1. (a)What is a solenoid ? When a current is passed through a long, hollow and straight solenoid, a magnetic field is produced. Where is the strength of the magnetic field produced maximum and what is the pattern of the magnetic field at this place ?
2. (b)State Fleming's Left Hand Rule. Apply this rule to solve the following problem : A straight conductor is placed in east-west direction in a uniform magnetic field. If on passing current from east to west, the conductor moves towards north, what is the direction of magnetic field ?
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A solenoid's field is maximum and uniform inside it; for the given conductor, the magnetic field is directed vertically upwards.
(a) A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. The strength of the magnetic field it produces is **maximum inside** the solenoid, and at that place the field lines are straight, parallel to the axis and equally spaced — that is, the field there is **uniform**, having the same magnitude and direction at every point inside. (b) Fleming's Left Hand Rule: stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular; if the forefinger points along the magnetic field and the middle finger along the current, the thumb points along the force, that is the direction of motion of the conductor. Applying it with the middle finger pointing west (current from east to west) and the thumb pointing north (the observed motion), the forefinger points vertically upwards. Hence the magnetic field is directed **vertically upwards**.

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Q205 CBSE 2022
As shown in the diagram an aluminium rod ‘AB’ is suspended horizontally between the two poles of a strong horse shoe magent in such a way that the axis of rod is horizontal and the direction of the magnetic field is vertically upward. The rod is connected in series with a battery and a key. State giving reason :
1. (a)What is observed when a current is passed through the aluminum rod from end B to end A ?
2. (b)What change is observed in a situation in which the axis of the rod ‘AB’ is moved and aligned parallel to the magnetic field and current is passed in the rod in the same direction ?
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(a) The rod is displaced, as the current is perpendicular to the field; (b) it stays at rest, as the current is parallel to the field.
(a) The aluminium rod AB is displaced: it swings sideways, towards the left in this arrangement. Reason: a current-carrying conductor placed in a magnetic field experiences a force. Here the current (from B to A) is at right angles to the field (vertically upward), so the force is the greatest possible and acts at right angles to both the rod and the field. Its direction is given by Fleming's left-hand rule: forefinger along the field (upward), middle finger along the current (B to A), and the thumb gives the force (to the left). (b) The rod is no longer displaced; it stays at rest. Reason: when the rod, and so the current, is parallel to the magnetic field, no force acts on it. The force is greatest when the current is at right angles to the field and becomes zero when the current is along the field ( $F = B I L sin 0^{\circ} = 0$ ).

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Q206 CBSE 2022

“Magnetic field is a physical quantity that has both direction and magnitude.” How can this statement be proved with the help of magnetic field lines of a bar magnet ?

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A field line's tangent gives the field direction and the closeness of lines gives its strength, so the field has direction and magnitude.
The magnetic field lines of a bar magnet show both properties. Direction: each field line carries an arrow. Outside the magnet the lines emerge from the north pole and merge at the south pole, and inside it they run from the south pole to the north pole. The tangent to a field line at any point gives the direction of the field there: a compass needle placed at that point sets itself along the line, its north end pointing along the arrow. No two lines cross, since the field cannot have two directions at one point. Magnitude: the relative strength of the field is shown by the closeness of the lines. The lines are crowded near the poles, where the field is stronger, and spread apart farther away, where it is weaker. Since the field lines give a direction and a strength at every point, the magnetic field is a quantity that has both direction and magnitude.

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Q207 CBSE 2022
1. (i)Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
2. (ii)An alpha particle while passing through a magnetic field gets projected towards north. In which direction will an electron project when it passes through the same magnetic field ?
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(i) Fleming's left-hand rule; (ii) the electron is deflected towards the south, opposite to the alpha particle.
(i) 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 (first finger) points in the direction of the magnetic field and the middle (second) finger in the direction of the current, then the thumb points in the direction of the force on the conductor, that is, the direction in which it moves. (ii) Towards the south. The alpha particle is positively charged and the electron negatively charged, so an electron moving the same way through the same field amounts to a current in the opposite direction; by Fleming's left-hand rule the force on it is reversed, from north to south.

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Q208 CBSE 2022
1. (a)Name the poles P, Q, R and S of the magnets in the following figures ‘a’ and ‘b’ :
2. (b)State the inference drawn about the direction of the magnetic field lines on the basis of these diagrams.
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P and R are north poles, Q and S are south poles; outside a magnet the field lines run from north to south.
(a) Figure ‘a’: P is the north pole and Q is the south pole. Figure ‘b’: R is a north pole and S is a south pole. (b) The field lines leave P and R and enter Q and S. Inference: outside a magnet, magnetic field lines emerge from the north pole and merge at the south pole, that is, their direction outside the magnet is from the north pole to the south pole. (Inside the magnet they run from the south pole to the north pole, so the field lines are closed curves.)

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Q209 CBSE 2022
1. (i)A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased ? What does it indicate ?
2. (ii)State Right hand thumb rule.
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(i) The deflection increases, showing the field strengthens with the current; (ii) thumb along the current, wrapped fingers give the field direction.
(i) The deflection of the compass needle increases when the current in the wire is increased. This indicates that the strength of the magnetic field produced by the current at a given point increases as the current through the wire increases - the magnetic field depends directly on the current. (ii) Right-hand thumb rule: Imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points in the direction of the current. Then your fingers wrap around the conductor in the direction of the field lines of the magnetic field.

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Q210 CBSE 2022

What is a magnetic field ? How is the direction of a magnetic field at a place determined ?

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The field is the region around a magnet where its force acts; a compass needle's north pole shows its direction.
A magnetic field is the region surrounding a magnet in which the force of the magnet can be detected. It has both magnitude and direction. The direction of the magnetic field at a place is found by placing a small magnetic compass there. The needle turns and settles along the field, and the direction in which the north pole of the compass needle points (moves) is taken as the direction of the magnetic field at that place. For this reason the field lines outside a magnet are drawn from its north pole to its south pole.

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Q211 CBSE 2022
1. (i)What is a solenoid ?
2. (ii)Draw the pattern of magnetic field lines of the magnetic field produced by a solenoid through which a steady current flows.
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A solenoid is a closely wound coil of many turns; its field is uniform inside and like a bar magnet's outside.
(i) A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. (ii) The pattern is shown in the figure. Inside the solenoid the field lines are straight, parallel to its axis and evenly spaced, which shows that the field inside is uniform. Outside, the lines come out of one end, curve round the coil and go into the other end, as in the field of a bar magnet: the end the lines come out of is the north pole, the end they enter is the south pole, and inside the coil the lines run from S to N, so every line is a closed loop. The N end is the one at which the current, seen from that end, flows anticlockwise. No two field lines cross.

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Q212 CBSE 2022
When is the force experienced by a current – carrying straight conductor placed in a uniform magnetic field.
1. (i)Maximum ;
2. (ii)Minimum ?
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The force is maximum when the current is perpendicular to the field and minimum (zero) when it is parallel to the field.
(i) The force is maximum when the conductor is placed so that the direction of the current is at right angles (perpendicular) to the direction of the magnetic field. (ii) The force is minimum - zero - when the conductor is placed along the magnetic field, that is, when the direction of the current is parallel (or antiparallel) to the direction of the field.

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Q213 CBSE 2022

List two factors on which the strength of magnetic field at a point due to a current carrying straight conductor depends. State the rule that determines the direction of magnetic field produced in this case.

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The field depends on the current and on the distance from the conductor; its direction follows the right-hand thumb rule.
Two factors: (1) the magnitude of the current flowing through the conductor - the larger the current, the stronger the magnetic field at the point; (2) the distance of the point from the conductor - the farther the point, the weaker the field. The direction of the magnetic field is given by the right-hand thumb rule: hold the current-carrying straight conductor in your right hand with the thumb pointing in the direction of the current; the direction in which your fingers wrap round the conductor gives the direction of the magnetic field lines. (This rule is also known as Maxwell's corkscrew rule.)

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Q214 CBSE 2022

What is the pattern of the magnetic field lines produced by a current carrying straight conductor ? State the rule that determines the direction of the magnetic field in this case.

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Concentric circles centred on the conductor, in planes perpendicular to it; the direction follows the right-hand thumb rule.
Pattern: The magnetic field lines around a current-carrying straight conductor are concentric circles centred on the conductor, lying in planes perpendicular to it. The circles are closer together near the conductor, where the field is stronger, and farther apart away from it. Rule: The direction of the field is given by the right-hand thumb rule. If the conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers wrapped around the conductor give the direction of the magnetic field lines. For a vertical wire with current flowing upwards, the circles run anticlockwise when seen from above.

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Q215 CBSE 2022
1. (a)Draw the pattern of magnetic field lines around a bar magnet. Mark the position of North Pole, South Pole and the places where the magnetic field is strongest.
2. (b)Why do the magnetic field lines not intersect each other ?
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Lines go from N to S outside, are closest at the poles (strongest field) and never cross, as a point has one field direction.
(a) The drawing shows a bar magnet with its north pole (N) at one end and its south pole (S) at the other. Field lines emerge from the north pole, curve round outside the magnet and merge at the south pole, and inside the magnet they run from S to N, so each line is a closed curve; the arrowheads point from N to S outside the magnet. The lines are closest together near the two poles, so the magnetic field is strongest there, and the regions round N and S are marked; away from the magnet the lines spread apart and the field is weaker. No two lines cross. (b) The direction of the magnetic field at a point is the direction of the tangent to the field line there, the direction in which a compass needle placed at that point points. If two field lines intersected, the field at the point of intersection would have two directions, and the compass needle would have to point in two directions at once, which is not possible. Hence magnetic field lines never intersect each other.

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Q216 CBSE 2022

What is a Solenoid ? Draw the pattern of the magnetic field lines around a current carrying solenoid. Mark on the pattern the region where the magnetic field is uniform.

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A solenoid is a closely wound coil; inside, its field lines are parallel and equally spaced, giving a uniform field.
A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Pattern (see the figure): inside the solenoid the field lines are straight, parallel and equally spaced, running along its axis from one end to the other; outside, they come out of one end, curve round the solenoid and enter the other end, just like the field lines of a bar magnet. The end the lines come out of behaves as the north pole and the other end as the south pole; the lines never cross. Region of uniform field: the space inside the solenoid, away from its two open ends (shaded in the figure). There the field lines are parallel straight lines, equally spaced, which shows that the magnetic field is the same in magnitude and direction at all points.

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Q217 CBSE 2022
1. (i)What is a Solenoid ? What does the divergence of magnetic field lines near the ends of a current carrying solenoid indicate ?
2. (ii)How is an electromagnet made using a current carrying solenoid ?
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Diverging field lines at the ends of a solenoid mean a weaker field there; a soft iron core inside it makes an electromagnet.
(i) A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. The closeness of field lines shows the strength of a magnetic field, and near the ends of a current-carrying solenoid the field lines spread apart (diverge). This indicates that the magnetic field becomes weaker near the ends than inside the solenoid, where the lines are close, parallel and evenly spaced (a strong field, uniform in NCERT's account of a long solenoid). The lines come out of one end and go into the other, so the two ends behave like the north and south poles of a bar magnet. (ii) A rod of soft iron is placed inside a solenoid, that is, the insulated copper wire is wound round a soft iron core, and a current is passed through the coil from a battery through a key. The strong magnetic field inside the solenoid magnetises the soft iron, which then acts as a magnet, an electromagnet, for as long as the current flows.

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Q218 CBSE 2022
1. (i)State Fleming’s left hand rule.
2. (ii)Write the principle of working of an electric motor.
3. (iii)Write the function of (i) brushes, and (ii) split ring in an electric motor.
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A motor works because a current-carrying conductor in a magnetic field feels a force; brushes supply current, the split ring reverses it.
(i) 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 force on (the motion of) the conductor. (ii) An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. In the motor, the two arms of a current-carrying rectangular coil placed between the poles of a magnet carry currents in opposite directions, so they are pushed in opposite directions (one up and one down, by Fleming’s left-hand rule) and the coil rotates, converting electrical energy into mechanical energy. (iii) Brushes: the two stationary conducting brushes press against the two halves of the split ring and connect the rotating coil to the battery, so that current flows into and out of the coil while it turns. Split ring: it acts as a commutator; it reverses the direction of the current in the coil after every half rotation, so that the coil keeps rotating in the same direction.

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Q219 CBSE 2022
1. (a)Draw the pattern of magnetic field lines produced by a current carrying circular loop showing the direction of current in the loop and the direction of the magnetic field lines.
2. (b)State the rule which can be applied to know the direction of magnetic field lines in the above case.
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Field lines are concentric circles round the loop wire, straight and parallel at the centre; the right-hand thumb rule gives their direction.
(a) The pattern is drawn in the figure. With the loop perpendicular to the page, the current comes out of the page at the top of the loop ( $⊙$ ) and goes into it at the bottom ( $\otimes$ ). Near each of these points the field lines are concentric circles around the wire, anticlockwise round the top and clockwise round the bottom, becoming larger farther from the wire. Inside the loop both sets point the same way, so at the centre the lines are nearly straight and parallel, along the axis of the loop. (b) The right-hand thumb rule: hold the current-carrying conductor in the right hand with the thumb pointing along the current; the direction in which the fingers wrap around the conductor gives the direction of the magnetic field lines. It is also called Maxwell's corkscrew rule.

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Q220 CBSE 2022
1. (a)A student wants to use an electric heater, an electric bulb and an electric fan simultaneously. How should these gadgets be connected with the mains ? Justify your answer giving three reasons.
2. (b)What is an electric fuse ? How is it connected in a circuit ?
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Connect them in parallel across the mains; a fuse is a safety wire that melts on excess current and is connected in series.
(a) The heater, the bulb and the fan should be connected in parallel with the mains, each between the live and the neutral wire with its own switch. Reasons: (1) In parallel each gadget gets the full mains voltage, $220$ V, that it is designed to work on; in series the $220$ V would be shared among them. (2) Each gadget can be switched on or off independently, and if one of them fails or is switched off the others keep working; in series one break stops all of them. (3) Each gadget draws the current it needs according to its own resistance, the heater a large current and the bulb and the fan much smaller ones, whereas in series the same current would have to flow through all three, which cannot suit them all; the total resistance of the parallel combination is also less than that of any one gadget. (b) An electric fuse is a safety device that protects the circuit and the appliances by stopping the flow of any unduly high electric current. It is a piece of wire made of a metal or an alloy of appropriate melting point; if a current larger than its rating flows, the wire heats up, melts and breaks the circuit. The fuse is connected in series with the device or circuit it protects (in a house, in the live wire), so that the whole current passes through it.

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