13. Magnetic Effects of Electric current SEBA/ASSEB Class 10 Science– Important Questions and Answers | Assam HSLC
SEBA/ASSEB Class 10 Science Chapter 13: Magnetic Effects of Electric current Important Questions and Answers | HSLC Assam
Chapter 13: Magnetic Effects of Electric current
Multiple Choose Question and Answer :
3. Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a) is zero. (b) decreases as we move towards its end.
(c) increases as we move towards its end. (d) is the same at all points.
Answer : (d) is the same at all points.
[ Inside a long straight solenoid carrying current, the magnetic field is uniform and its strength is the same at all points along the axis of the solenoid.]
3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south (b) towards east (c) downward (d) upward
Answer: (c) Downward .
[ According to Fleming’s Left-Hand Rule, the direction of force on a positive charge is given by the direction of the magnetic force. Therefore, the magnetic field must be vertically downward.]
Question: A person got a severe electric shock while touching a refrigerator. The reason could might be - [2026]
(i) the domestic circuit has no proper earthing . (ii) the refrigerator may be of manufacturing defect.
(iii) due to flow of extra current to the appliance. (iv) due to fluctuation of voltage in supply mains.
Choose the correct option from the following.
(a) Only (i) is correct (b) (i) and (ii) both are correct.
(c) (ii) and (iii) are correct. (d) (i) and (iv) are correct .
Answer: (b) (i) and (ii) both are correct.
Question : When electric current is passed through the coil of a solenoid, then the magnetic field [SEBA 2023]
(a) increase along the direction of current . (b) decrease along the direction of current
(c) remains the same at all times (d) becomes zero
Answer : (a) Increase along the direction of the current.
[ When an electric current is passed through the coil of a solenoid, the magnetic field around the solenoid increases along the direction of the current. ]
20. Which among the following diagrams correctly represents the current-carrying wire and the magnetic field associated with it ? [2024]
(a) (b) (c) (d)
21. Which of the following correctly describes the magnetic field near a long straight wire ? [2024]
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of concentric circles centred on the wire.
(d) The field consists of radial lines originating from the wire.
Answer: (c) The field consists of concentric circles centred on the wire.
[ For a long straight current-carrying wire, the magnetic field lines form concentric circles around the wire, as described by the right-hand grip rule.]
Question : In electric generator , energy converted from 
energy to energy . [SEBA 2023]
Answer : mechanical ; electrical
Question: The device used for producing electric current is called [2025]
(a) motor (b) ammeter (c) galvanometer (d) generator
Answer: (d) generator.
[ A generator is the device that converts mechanical energy into electrical energy, thereby producing electric current.]
Question: A metal rod PQ is placed in the magnetic field. The ends of the rod are connected with a battery using wires . Where will the rod move ? [2025]
Photo
(a) Upward (b) Downward (c) Into the field (d) Out of the field
Answer:
Question: The magnetic field lines of solenoid are similar to the magnetic field lines of bar magnet . Which diagram correctly shows the solenoid as a bar magnet ? [2025]
Photo
(a) (b) (c) (d)
4. Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution.
Answer : (b) one revolution.
[ When a rectangular coil of copper wires is rotated in a magnetic field, the direction of the induced current changes once in each revolution.]
Very Short Question and Answer: [ 1 Mark ]
1. State Fleming’s left-hand rule.
Answer : Fleming's left-hand rule states: Stretch the thumb, forefinger and middle finger of your left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
2. What is the principle of an electric motor?
Answer: Answer: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming’s left-hand rule.
3. Which sources produce alternating current?
Answer: AC generators and domestic electric mains are sources of alternating current .
2. Name some sources of direct current.
Answer: Electric cells, batteries and DC generators are some sources of direct current.
1. State the principle of an electric generator.
Answer: An electric generator works on the principle of electromagnetic induction. It converts mechanical energy into electrical energy.
2. A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?
Answer : At a point directly below the horizontal power line, the direction of the magnetic field is vertically upward.
Short Question and Answer: [ 2 Marks ]
1. Why does a compass needle get deflected when brought near a bar magnet?
Answer: A compass needle gets deflected when brought near a bar magnet due to the magnetic field produced by the magnet. The compass needle aligns itself with the magnetic field lines, indicating the presence and direction of the magnetic field.
3. Why don’t two magnetic lines of force intersect each other?
Answer: Two magnetic field lines never intersect each other because, if they did, the compass needle at the point of intersection would point in two different directions at the same time, which is impossible.
2. List the properties of magnetic lines of force.
Answer: The properties of magnetic lines of force are:
(i) They always form closed loops, emerging from the north pole and entering the south pole.
(ii) They never intersect each other.
(iii) The density of lines indicates the strength of the magnetic field.
(iv) They repel each other in a uniform field.
(v) They are directed from the north to the south pole outside the magnet.
15. Explain the working function of an electric motor . [2M 2019]
Answer: When current is passed through the coil placed in a magnetic field, the two sides of the coil experience forces in opposite directions . These forces form a couple and rotate the coil. The split ring (commutator) reverses the direction of current after every half rotation, so the coil continues to rotate in the same direction. Thus, electrical energy is converted into mechanical energy.
16. What is the role of the split rings in an electric motor ? [2M SEBA 2020]
Answer: The split ring acts as a commutator. It reverses the direction of current in the coil after every half rotation. Due to this, the direction of force on the coil also reverses and the coil continues to rotate in the same direction.
22. Explain the underlying principle of an electric generator by drawing a labeled diagram .[2M 2016]
Answer: The underlying principle of an electric generator is electromagnetic induction. When a coil is rotated in a magnetic field, the magnetic field lines linked with the coil keep changing continuously, which induces an electromotive force in the coil. In a simple AC generator, a rectangular coil ABCD is rotated between the poles of a strong magnet; as it turns, the arms AB and CD move across the magnetic field and a current is induced. The direction of the induced current reverses every half rotation, so the current produced is alternating current (AC). In an Indian household circuit, this current reverses direction every 1/100 second, giving a frequency of 50 Hz.
Photo
23. (a) State the rule which is used to know the direction of induced current in a coil . [2M 2016]
(b) Draw the magnetic field lines when current passes through a circular coil.
Answer: (a) The direction of induced current in a coil is determined by Fleming's right-hand rule.
Fleming's right-hand rule: Stretch the thumb, forefinger and middle finger of the right hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the thumb points in the direction of motion of the conductor, then the middle finger gives the direction of the induced current.
(b) Photo
20.How does solenoid behave like a magnet ? Explain with diagram [2M 2017]
Answer: A solenoid behaves like a bar magnet when electric current flows through it. One end acts as the north pole and the other acts as the south pole depending on the direction of current. The magnetic field lines inside the solenoid are parallel straight lines which indicate a uniform magnetic field. Outside the solenoid the field lines curve like those of a bar magnet.
20. (a) What is electromagnetic induction ? [2M 2017]
(b) Write the principal difference between AC generator and DC generator .
Answer: (a) The phenomenon of producing electric current in a coil by changing the magnetic field around it is called electromagnetic induction.
(b) The principal difference between AC generator and DC generator are :
|
AC Generator |
DC Generator |
|
(i) It produces alternating current, which reverses direction periodically. |
(i) It produces direct current, which flows in one direction only. |
|
(ii) It uses two slip rings to connect the coil to the external circuit. |
(ii) It uses a split-ring commutator (two half-rings) to connect the coil. |
|
(iii) The ends of the coil are connected to separate slip rings. |
(iii) The ends of the coil are connected to the two halves of the commutator. |
|
(iv) The current in the external circuit changes direction after every half rotation. |
(iv) The commutator reverses the connection every half rotation, so the current in the external circuit stays in one direction. |
22. State the basic principle of an electric motor. What is the function of a split ring in an electric motor ? [2M 2018]
Answer: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force which causes it to rotate.
The split ring acts as a commutator. It reverses the direction of current in the coil after every half rotation so that the coil continues to rotate in the same direction.
23. Write two precautions taken to avoid the overloading of domestic electric circuits. [2M 2018]
Answer: Two precautions to avoid overloading of domestic electric circuits are:
(i) We should not connect too many electrical appliances to a single socket.
(ii) We should avoid using many high-power electrical appliances at the same time in a single circuit.
53. Explain two ways to induce current in a coil . [2M 2024]
Answer: Current can be induced in a coil in two ways:
(i) by moving a bar magnet towards or away from the coil, so that the magnetic field linked with it changes;
(ii) by keeping the magnet stationary and moving the coil towards or away from it.
Long Question and Answer: [3 Marks , 4 Marks and 5 Marks]
25. Explain how does a Solenoid behave like a magnet . When is the force experienced by a current-carrying conductor placed in a magnetic field largest ? [3M 2019]
Answer: When current is passed through a solenoid, a magnetic field is produced around it. The field lines inside the solenoid are parallel straight lines, indicating a uniform magnetic field. One end of the solenoid behaves like a north pole and the other end like a south pole, just like a bar magnet. Hence, a current-carrying solenoid behaves like a bar magnet.
The force experienced by a current-carrying conductor placed in a magnetic field is largest when the conductor is placed perpendicular to the direction of the magnetic field.
15. Distinguish between electric generator and electric motor. Explain the functions of (i) the brush ring in electric generator and (ii) slip rings in electric motor. [3M 2015]
Answer: The difference between an Electric Generator and an Electric Motor :
|
Electric Generator |
Electric Motor |
|
It converts mechanical energy into electrical energy. |
It converts electrical energy into mechanical energy. |
|
It works on the principle of electromagnetic induction. |
It works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. |
(i) Brush rings in an electric generator: The carbon brushes maintain contact with the rotating rings and help transfer the induced electric current from the generator to the external circuit.
(ii) Slip rings in an electric motor: The slip rings maintain electrical contact between the rotating coil and the external circuit. They allow current to flow through the coil while it rotates, enabling the motor to work continuously.
15. Explain the phenomenon of electromagnetic induction with an experiment . [3M 2015]
Answer: The phenomenon of producing electric current in a coil by changing the magnetic field around it is called electromagnetic induction.
Photo
Take a coil of wire AB having a large number of turns and connect its ends to a galvanometer. Now, move the north pole of a strong bar magnet towards end B of the coil. The galvanometer shows a momentary deflection, indicating that an electric current is induced in the coil. When the magnet stops moving, the deflection becomes zero. Now, withdraw the magnet away from the coil. The galvanometer deflects in the opposite direction, showing that the current flows in the opposite direction. Similarly, when the magnet is kept stationary and the coil is moved towards or away from it, the galvanometer shows deflections in opposite directions. When both the coil and the magnet remain stationary with respect to each other, there is no deflection in the galvanometer.
This experiment shows that an electric current is induced in a coil whenever there is a change in the magnetic field around it. This phenomenon is called electromagnetic induction.
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