Class 10 Science Chapter 12: Magnetic Effects of Electric Current worksheet with answer key
A 20-mark worksheet on Magnetic Effects of Electric Current for about 40 minutes of class or homework: 5 multiple-choice, 3 very short answer and 3 short answer questions, written from the NCERT chapter and checked by a second reviewer. Print the PDF for the class; the answer key carries the marking scheme. Teachers may photocopy it freely.
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Answer: (a) adding one more cell in series to increase the current
The field at a point increases as the current increases, so an extra cell gives a larger deflection. Lifting the compass moves it farther from the wire, where the field is smaller; removing a cell lowers the current; reversing the battery only reverses the direction.
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Answer: (c) deflects towards the west
Reversing the current reverses the direction of the field it produces, so the needle deflects the opposite way, towards the west.
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Answer: (c) at P, because the lines are closer together there
The relative strength of the field is shown by how close the lines are: they are crowded near P and spread out near Q, so the field is stronger at P.
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Answer: (b) magnetic field
The region surrounding a magnet in which its force can be detected is its magnetic field. A field line is only one path drawn in that region.
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Answer: (b) Oersted, in 1820
Oersted saw the compass needle deflect when a current was passed through a nearby wire, in 1820. Ampere's contribution came later and concerned the force on the conductor.
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(a) Maxwell's corkscrew rule, another name for the right-hand thumb rule. (b) A corkscrew driven downwards turns clockwise as seen from above, so the field lines go round the wire clockwise when viewed from above.
- Maxwell's corkscrew rule (1)
- clockwise seen from above (1)
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(a) An equal and opposite force: the magnet exerts on the current-carrying wire a force equal in size to the force on the magnet and opposite in direction. (b) Andre Marie Ampere.
- equal and opposite force on the wire (1)
- Ampere (1)
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The wires pass through the main fuse into the electricity meter, and then through the main switch to the line wires of the house.
- main fuse, then the electricity meter (1)
- main switch, before the line wires (1)
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(a) The unduly high current produces Joule heating in the fuse wire, which melts it and breaks the circuit. (b) In series, all the current of the circuit passes through the fuse, so any excess current melts it; across the appliances it would not carry the whole current. (c) In parallel, each appliance is connected across the live and neutral wires, so every appliance gets the same potential difference and has its own switch.
- Joule heating melts the fuse and breaks the circuit (1)
- in series all the current passes through the fuse (1)
- parallel gives every appliance the same potential difference (1)
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(a) The coil is a solenoid; the field lines inside it are parallel straight lines, so the field inside is uniform. (b) The strong field inside the current-carrying solenoid magnetises the soft-iron nail placed in it, so the nail itself becomes a magnet and lifts many more pins. (c) An electromagnet, a soft-iron core wrapped with a coil of insulated copper wire.
- solenoid; uniform field of parallel straight lines inside (1)
- field inside magnetises the soft-iron nail (1)
- electromagnet (1)
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(a) Magnetic field lines: each is the path along which a free north pole would tend to move. (b) At each point the field is in the direction in which the north pole of the compass points, so he puts the arrow that way. (c) The field is strongest where the lines are most crowded, that is, closest together.
- magnetic field lines, the path of a free north pole (1)
- arrow in the direction the north pole of the compass points (1)
- strongest where the lines are closest together (1)