CBSE Class 10 Science Magnetic Effects of Electric Current MCQs Set 11

Answer: (d) perpendicular to the plane of the wire

Explanation:
1. Near the centre of a circular loop the field lines are nearly straight.
2. These straight lines are perpendicular to the plane of the loop.

Teacher's Note:
1. The face of the loop acts as a pole, so the field is along the axis.
2. Direction follows the clock rule.

Answer: (d) either (a) or (b)

Explanation:
1. A compass needle placed near an end of the solenoid is attracted or repelled, which shows the pole.
2. The clock rule or right-hand rule applied to the current direction also gives the pole.
3. Fleming's left-hand rule gives force, not poles. So the answer is either (a) or (b).

Teacher's Note:
1. The north end of a compass needle is repelled by a north pole.
2. Clock rule: anticlockwise current gives a north pole.

Answer: (d) east

Explanation:
1. Use the right-hand thumb rule with the thumb pointing north along the current.
2. Above the wire the curled fingers point from west to east, so the field is towards the east.

Teacher's Note:
1. Below the wire the field is in the opposite direction.
2. Picture the field circles around the wire.

Answer: (d) The magnetic field produced by the passage of current through a straight wire is permanent.

Explanation:
1. The field of a wire exists only while the current flows.
2. So the statement that it is permanent is not true.
3. The other three are correct.

Teacher's Note:
1. No current means no field.
2. Electromagnets are temporary magnets.

Answer: (a) a magnetic field

Explanation:
1. The region around a magnet in which its force can be detected is called its magnetic field.

Teacher's Note:
1. Field lines show the direction and strength.
2. Poles are the ends of the magnet.

Answer: (c) both (a) and (b)

Explanation:
1. The field circles around the wire become larger and larger as we move away from it.
2. At the centre of the loop the circles are so large that they look like straight lines.
3. So both statements are true.

Teacher's Note:
1. The field at the centre is straight and perpendicular to the loop.
2. The field is strongest at the centre.

Answer: (b) repulsion

Explanation:
1. Attraction also occurs between a magnet and an unmagnetised piece of iron.
2. Repulsion occurs only between two like magnetic poles, so it is the sure test of a magnet.

Teacher's Note:
1. Attraction alone does not prove a magnet.
2. Repulsion proves it.

Answer: (b) north to south

Explanation:
1. Hold the wire in the right hand with the thumb pointing west.
2. Below the wire, the fingers point from north to south.

Teacher's Note:
1. Above the wire the field points the other way.
2. Use the thumb rule.

Answer: (b) electric charges in motion

Explanation:
1. Moving charges form a current, and a current produces a magnetic field.
2. Charges at rest do not.

Teacher's Note:
1. Oersted: current gives a magnetic field.
2. Permanent magnets are not the only source.

Answer: (c) (A) only

Explanation:
1. A is true: the field lines are closed circles, so there are no poles.
2. B is false: the lines are circles, not straight.
3. C is false: a smaller radius gives a stronger field at the centre.
4. So only A is correct.

Teacher's Note:
1. Field at the centre is inversely proportional to the radius.
2. Straight wire gives circular lines.

Answer: (b) settle as circles

Explanation:
1. The field around a straight wire is a set of concentric circles.
2. The filings arrange themselves along these circles.

Teacher's Note:
1. This is the standard activity for the field of a straight wire.
2. The circles get larger away from the wire.

Answer: (c) Field lines are continuous lines passing inside and outside the magnet. Only one field line passes through any given point.

Explanation:
1. Field lines are closed, continuous curves going through the magnet and outside it.
2. Two lines cannot cross, so only one line passes through any point.

Teacher's Note:
1. Lines never start or end.
2. They never intersect.

Answer: (b) (B) only

Explanation:
1. Statement A is false: like poles repel and unlike poles attract.
2. Statement B is true: a magnet always has both poles.

Teacher's Note:
1. Cutting a magnet gives two magnets.
2. Check each statement.

Answer: (b) Steel

Explanation:
1. A permanent magnet must keep its magnetism after the magnetising field is removed.
2. Steel retains magnetism, so it is used for permanent magnets.

Teacher's Note:
1. Soft iron: temporary magnets. Steel: permanent magnets.
2. Copper is not magnetic.

Answer: (d) MRI: magnetic resonance imaging

Explanation:
1. The right-hand thumb rule gives the direction of the magnetic field, not of force.
2. A galvanometer detects current; it does not adjust it.
3. The earth wire has green insulation (green or green/yellow).
4. MRI stands for magnetic resonance imaging, so (d) is correct.

Teacher's Note:
1. MRI uses strong magnetic fields to image the body.
2. Remember: red or brown is live, green is earth.

Answer: (c) Magnetic Resonance Imaging

Explanation:
1. MRI is a medical technique that uses a strong magnetic field to form pictures of the organs inside the body.
2. Its full form is Magnetic Resonance Imaging.

Teacher's Note:
1. It is an application of magnetism in medicine.
2. It does not use X-rays.

Answer: (b) (iii) and (iv)

Explanation:
1. A moving charge produces both an electric field and a magnetic field, so (i) is false.
2. A charge feels a force in an electric field as well, so (ii) is false.
3. The field inside a solenoid is uniform, so (iii) is true.
4. Field lines are closed curves, so (iv) is true.
5. Hence (iii) and (iv) are correct.

Teacher's Note:
1. Test every statement separately.
2. Uniform field inside a solenoid and closed lines are standard facts.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Both statements are true: the field falls with distance from the wire.
2. R gives the reason for A, because B is inversely proportional to the distance.

Teacher's Note:
1. Use B ∝ 1/r for a long straight wire.
2. Field lines are more crowded near the wire.

Answer: (c) A is true, but R is false.

Explanation:
1. The filings line up along the field lines, so A is true.
2. The magnetic field has both magnitude and direction, so it is a vector. R is false.

Teacher's Note:
1. Iron filings show the pattern of field lines.
2. Field is a vector, not a scalar.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. If two field lines crossed, the compass needle at that point would have two directions.
2. This is impossible, so R correctly explains A.

Teacher's Note:
1. One point, one field direction.
2. Learn this reason by heart.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. The current produces a magnetic field around the wire.
2. This field acts on the compass needle and deflects it, so R explains A.

Teacher's Note:
1. This is Oersted's experiment.
2. Reversing the current reverses the deflection.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Field lines never cross, because a point cannot have two field directions, so A is true.
2. Field lines are closed curves, so R is also true.
3. But the closed shape of the lines is not the reason why they do not cross, so R is not the explanation.

Teacher's Note:
1. The correct reason is: two directions at one point are impossible.
2. Check whether R really explains A.

Answer: (c) A is true, but R is false.

Explanation:
1. Current in the wire produces a magnetic field, which deflects the compass needle, so A is true.
2. The SI unit of magnetic field is the tesla, not the oersted, so R is false.

Teacher's Note:
1. SI unit of magnetic field: tesla (T).
2. Oersted discovered the effect; do not confuse him with the unit.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. A compass needle is a small magnet, whose north end points along the field, so A is true.
2. It does get deflected near a bar magnet, so R is true.
3. But this deflection does not explain why a compass shows the field direction.

Teacher's Note:
1. The needle lines up with the field at its position.
2. A compass is a small pivoted magnet.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. The field of a current-carrying coil is directly proportional to the current.
2. So doubling the current doubles the field, and R explains A.

Teacher's Note:
1. More current gives a stronger field.
2. More turns also give a stronger field.

Answer: (c) A is true, but R is false.

Explanation:
1. The field on the axis is greatest at the centre of the coil, so A is true.
2. The field decreases as the distance from the coil increases; it is not proportional to the distance. So R is false.

Teacher's Note:
1. Field is strongest at the centre of the loop.
2. It falls with distance.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Unlike poles attract each other, so the force helps to bring the poles together.
2. Hence A is true, and R explains it.

Teacher's Note:
1. Like poles repel; unlike poles attract.
2. Bringing like poles together needs effort.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. A larger current gives a stronger field, so A is true.
2. Electromagnets are used to lift heavy iron objects, so R is true.
3. But R does not explain why the strength depends on the current.

Teacher's Note:
1. Check whether R really gives the reason.
2. Strength depends on current and number of turns.

Answer: (d) A is false, but R is true.

Explanation:
1. Steel is not used as a core, because it stays magnetised, so A is false.
2. Steel does become permanently magnetised, so R is true.

Teacher's Note:
1. The core should be soft iron.
2. An electromagnet must switch off when the current stops.

Answer: (c) A is true, but R is false.

Explanation:
1. Appliances with a metallic body use a third pin connected to the earth wire. This protects the user from electric shock, so A is true.
2. Three-pin connections do not reduce the heating of wires, so R is false.

Teacher's Note:
1. The earth pin is a safety feature.
2. An electric bulb has no metal body that needs earthing.