ActivityTake two different coils of copper wire havinglarge number of

1.	ActivityTake two different coils of copper wire havinglarge number of turns (say 50 and 100 turnsrespectively). Insert them over a non-conductingcylindrical roll, as shown in Fig. 13.17. (You mayuse a thick paper roll for this purpose.)Connect the coil-1. having larger number ofturns, in series with a battery and a plug key.Also connect the other coil-2 withgalvanometer as shown.Plug in the key. Observe the galvanometer. Isthere a deflection in its needle? You will observethat the needle of the galvanometer instantlyjumps to one side and just as quickly returns tozero. Indicating a momentary current in coll-2.Disconnect coil-1 from the battery. You willobserve that the needle momentarily moves, butto the opposite side. It means that now thecurrent flows in the opposite direction in coil-2.HHHO)Figure 13.17Current is induced in coil-2 inhen currentin coll-1 is changed
Answer» ANSWER Choose the INCORRECT statement from the following regarding magnetic lines of field (a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points (b) Magnetic field lines are closed curves (c) If magnetic field lines are parallel and equidistant, they represent zero field strength (d) Relative strength of magnetic field is shown by the degree of closeness of the field lines Soln: Answer is (c) If magnetic field lines are parallel and equidistant, they represent zero field strength Explanation: Option c) is incorrect because parallel lines of magnetic field represent uniform magnetic field. 2. If the KEY in the arrangement (Figure 13.1) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are (a) concentric circles (b) elliptical in shape (c) straight lines parallel to each other (d) concentric circles near the point O but of elliptical shapes as we go away from it Soln: Answer is (a) concentric circles EXPLAINATION When open magnetic field lines are drawn over the horizontal plane ABCD, , then the magnetic field lines will be in the FORM of concentric circles with centre at the axis of the conductor. This is because there will be no FLOW of current and therefore there will be no magnetic field due to the conductor. So, at point O. only Earth’s magnetic field will be present so the magnetic field lines will be in the form of concentric circles. 3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to (a) A (b) B (c) A if the current is small, and B if the current is LARGE (d) B if the current is small and A if the current is large Soln: Answer is (a) A Explanation: Direction of Magnetic field will be from south to northpole. Point A is showing northpole because field lines are pointing from B to A

ActivityTake two different coils of copper wire havinglarge number of turns (say 50 and 100 turnsrespectively). Insert them over a non-conductingcylindrical roll, as shown in Fig. 13.17. (You mayuse a thick paper roll for this purpose.)Connect the coil-1. having larger number ofturns, in series with a battery and a plug key.Also connect the other coil-2 withgalvanometer as shown.Plug in the key. Observe the galvanometer. Isthere a deflection in its needle? You will observethat the needle of the galvanometer instantlyjumps to one side and just as quickly returns tozero. Indicating a momentary current in coll-2.Disconnect coil-1 from the battery. You willobserve that the needle momentarily moves, butto the opposite side. It means that now thecurrent flows in the opposite direction in coil-2.HHHO)Figure 13.17Current is induced in coil-2 inhen currentin coll-1 is changed

Answer»

ANSWER

Choose the INCORRECT statement from the following regarding magnetic lines of field

(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a

magnetic compass needle points

(b) Magnetic field lines are closed curves

(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines

Soln:

Answer is (c) If magnetic field lines are parallel and equidistant, they represent zero field strength

Explanation:

Option c) is incorrect because parallel lines of magnetic field represent uniform magnetic field.

2. If the KEY in the arrangement (Figure 13.1) is taken out (the circuit is made open) and magnetic field

lines are drawn over the horizontal plane ABCD, the lines are

(a) concentric circles

(b) elliptical in shape

(d) concentric circles near the point O but of elliptical shapes as we go away from it

Soln:

Answer is (a) concentric circles

EXPLAINATION

When open magnetic field lines are drawn over the horizontal plane ABCD, , then the magnetic field lines will be

in the FORM of concentric circles with centre at the axis of the conductor. This is because there will be no FLOW of

current and therefore there will be no magnetic field due to the conductor. So, at point O. only Earth’s magnetic

field will be present so the magnetic field lines will be in the form of concentric circles.

3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is

ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti

clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the

resultant magnet is on the face close to

(a) A

(b) B

(d) B if the current is small and A if the current is large

Soln:

Answer is (a) A

Explanation:

Direction of Magnetic field will be from south to northpole. Point A is showing northpole because field lines are pointing from B to A

ANSWER

EXPLAINATION

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