Magnetic Effects of Electric Current
Multiple Choice Questions
- Which of the following correctly describes the magnetic field near a long straight wire ?
(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 radial lines originating from the wires
(d) The field consists of concentric circles centred on the wire.
- Which of the property of a proton can change while it moves freely in a magnetic field ? (There may be more than one correct answer.)
- Who gave cork screw rule (right land thumb rule)?
Ans. 1. (d), 2. (c) and (d), 3. (a).
Fill in the Blanks
- An electric current flowing through a conductor produces a field.
- Magnetic field is a quantity that has both and magnitude.
Ans. 1. magnetic, 2. direction.
- Field lines of terrestrial magnet are parallel.
- The magnetic field lines meet each other at end of the magnet.
- The field lines are dense near end of a bar magnet.
Ans. 1. True, 2. False, 3. True.
Match the Columns
Column A Column B
- Intensity of. . (a) Electromagnet
- Cork screw rule. (b) Oersted
- Temporary magnet. (c) Maxwell
Ans. 1. (b), 2. (c), 3. (a).
Answer in one Word/Sentence
- Is magnetic field a vector or a scalar quantity ?
Ans. Vector quantity as it has both magnitude and direction.
- Who discovered magnetic effect of current ?
Ans. Oersted in 1920,
- What happens when an electric current passes through a metallic conductor ?
Ans. An electric current through a metallic conductor produces a magnetic field around it.
Very Short Answer Type Questions
- 1. Why does a compass needle get deflected when brought near a bar magnet?
Ans: The compass needle is a small magnet. That is why, when brought near a bar magnet, its magnetic lines of force interact with the magnetic field lines of the bar magnet. Hence, the needle gets deflected.
- 2. Why don’t two magnetic lines of force intersect each other?
Ans. The two magnetic field lines do not intersect each other because if they will do so, then at the point of intersection, the compass needle will show two different directions, which is not possible.
- 3. List three sources of magnetic fields.
Ans. The sources of magnetic fields are:
(i) Current carrying conductors.
(ii) Permanent magnets
- 4. Write the names of three sources of direct current.
Ans. The sources of direct current :
(1) Direct current generator (D.C. Generator). (2) Chemical electric cells or batteries.
(3) Solar electric cells or batteries.
Short Answer Type Questions
- 1. Draw magnetic field lines around a bar magnet.
Ans. Magnetic field lines around a bar magnet
- 2. List the properties of magnetic lines of force.
Write any three properties of magnetic field lines.
Ans. The properties of magnetic lines of force are as follows:
(1) Magnetic field lines emerge from the north pole and merge at the south pole.
(2) The magnetic field lines are closed curves.
(3) The relative strength of the magnetic field is shown by the degree of closeness of the magnetic field lines. The closer these lines, the greater is the magnetic field.
(4) No two magnetic field lines cross each other or intersect.
(5) The direction of magnetic field lines inside the magnet is from the south pole to the north pole.
Long Answer Type / Analytical Questions
- 1. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current carrying solenoid with the help of a bar magnet ? Explain.
Ans. A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current carrying solenoid is shown in the Fig. 13.1.
In the fig, when the north pole of a bar magnet brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end
connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves a the north pole and the other end behaves as a south pole.