Download of magnetic flux? (1) Wb

Electromagnetic Induction
1
A student inserts a bar magnet into a coil connected to a galvanometer as shown.
A higher reading can be obtained by
(1) using a coil made of thinner wire.
(2) using a coil with more number of turns.
(3) moving the magnet at a higher speed.
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
Answer: D
2
A magnet is dropped through a solenoid as shown. The ends of the solenoid are
connected to a centre-zero galvanometer.
S
motion of magnet
N
A
solenoid
G
centre-zero galvanometer
hollow paper cylinder
B
At the instant as shown, what are the magnetic polarities of the ends A and B?
A
B
A.
N
S
B.
S
N
C.
N
no magnetic pole
D.
S
no magnetic pole
Answer: A
1
3
A magnet is dropped through a solenoid as shown. The ends of the solenoid are
connected to a centre-zero galvanometer.
S
motion of magnet
N
A
solenoid
G
centre-zero galvanometer
hollow paper cylinder
B
The maximum induced current can be increased by
(1) using a stronger magnet.
(2) using a solenoid with more number of turns.
(3) connecting a resistor in parallel with the centre-zero galvanometer.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
Answer: D
4
A solenoid is connected to a d.c. power supply as shown. When the switch is closed,
the ring jumps up. The ring can be made of
iron core
ring
d.c.
power
supply
(1)
(2)
(3)
A.
B.
C.
D.
aluminium.
iron.
plastic.
(2) only
(3) only
(1) and (2) only
(1), (2) and (3)
Answer: C
2
5
A coil connected to a galvanometer is placed between two electromagnets as shown.
N
electromagnet
centre-zero
galvanometer
G
S
The pointer of the galvanometer will not deflect when
A. the coil is moved towards the south pole of the electromagnet.
B. the coil is rotated through 180°.
C. the coil is moved to the left.
D. the electromagnet is turned off.
Answer: A
6
A piece of straight wire XY connected to a centre-zero galvanometer is placed inside a
magnetic field as shown.
Y
centre-zero
galvanometer
X
The wire XY is moved upwards and stops. Which of the following statements about
the pointer of the galvanometer is correct?
A. It shows no deflection.
B. It deflects and then remains stationary.
C. It deflects to one side and then returns to the centre position.
D. It deflects to one side and then deflects to another side. Finally, it returns to the
centre position.
Answer: C
3
7
The figure below shows a simple generator.
Which of the following graphs best shows the variation of the induced current I
against time t?
A.
I /A
0
C.
B.
t /s
0
I /A
0
I /A
D.
t /s
t /s
I /A
0
t /s
Answer: D
8
The figure below shows a simple generator.
Which of the following graphs best shows the variation of the induced current I
against time t?
4
A.
I /A
B.
0
C.
t /s
0
I /A
D.
0
I /A
t /s
t /s
I /A
0
t /s
Answer: C
9
A rectangular coil PQRS is moved with constant velocity in a direction perpendicular
to a uniform magnetic field as shown.
P
Q
S
R
Which of the following statements is/are correct?
(1) A voltage is induced across PS and QR respectively.
(2) The induced voltage becomes lower when the coil moves faster.
(3) An induced current flows along the coil in the clockwise direction PQRS.
A. (1) only
B. (2) only
C. (1) and (2) only
D. (1) and (3) only
Answer: A
5
10
An induction cooker makes use of eddy current to heat up a metal utensil, which in
turn, heats up the food it contains. The food can be heated up faster by
(1) increasing the strength of the alternating magnetic field produced by the
induction cooker.
(2) connecting the induction cooker to a voltage supply lower than its working
voltage.
(3) covering the utensil with a lid.
A. (2) only
B. (3) only
C. (1) and (2) only
D. (1) and (3) only
Answer: D
11
Two coils A and B wound on an iron core are connected into two circuits respectively
as shown above. Switch S is closed at time t1and then opened at time t2. Which of the
following best shows the directions of the currents passing through coil B at time t1
and time t2 respectively?
At time t1
At time t2
A.
6
B.
C.
D.
Answer: C
12
A soft-iron bar is push towards solenoid A as shown. The bar remains in the solenoid
afterwards.
G
soft-iron bar
solenoid A
solenoid B
Which of the following graphs best represents the induced current flowing through
solenoid B?
A. induced current / A
B. induced current / A
0
time / s
0
7
time / s
C. induced current / A
D. induced current / A
time / s
0
time / s
0
Answer: C
13
A solenoid, a battery and a switch S are connected into a circuit and an aluminium
ring is hung at one of the ends of the solenoid coaxially as shown. Initially, S is closed.
aluminium ring
W
X
Z
Y
S
If S is opened at a certain instant, what is the direction of motion of the ring?
A.
W
B.
X
C.
Y
D.
Z
Answer: D
14
A wire connected to a galvanometer is placed beside a straight current-carrying wire
as shown in figure a.
I/A
centre-zero
galvanometer
G
I
0
t/s
1
2
3
4
5
Figure a
Figure b
The current I in the straight wire varies as shown in figure b. Which of the following
graphs best represent the reading of the galvanometer?
8
A.
0
C.
B.
induced current / A
t/s
1
2
3
4
5
D.
induced current / A
0
t/s
1
2
3
4
5
Answer: B
15
A bar magnet is released from rest and it falls through a solenoid as shown.
bar magnet
solenoid
Which of the following graphs best shows how the velocity of the bar magnet varies
with time?
A. velocity / m s1
B. velocity / m s1
0
time / s
0
9
time / s
C. velocity / m s1
D. velocity / m s1
0
time / s
time / s
0
Answer: C
16
Which of the following is/are the unit(s) of magnetic flux?
(1)
Wb
(2)
N m A−1
(3)
T m2
A.
(1) only
B.
(1) and (3) only
C.
(2) and (3) only
D.
(1), (2) and (3)
Answer: D
17
A long straight wire carries a current I in vacuum. Consider a cylindrical surface of
radius r and length L with its central axis coincides with the wire as shown.
cylindrical surface
current-carrying
wire
Find the magnetic flux through the cylindrical surface.
A. 0
B. μ 0 IL
C. μ 0 Ir
μ 0 ILr
2
Answer: A
D.
18
A metal ring is placed in a uniform magnetic field with its plane perpendicular to the
field. The ring is cooled and contracts uniformly. A current is induced in the ring in
the anticlockwise direction as shown.
10
Which of the following statements is/are correct?
(1)
The magnetic field points out of the plane of the paper.
(2)
The resistance of the ring decreases.
(3)
The magnetic flux through the ring remains unchanged.
A.
(1) only
B.
(3) only
C.
(1) and (2) only
D.
(2) and (3) only
Answer: C
19
A square conducting loop, a 0.15 Ω resistor and an ammeter are connected into a
circuit a shown. A uniform magnetic field is applied perpendicularly to the loop and
its magnitude is decreasing at a constant rate of 6.00 × 10−2 T s−1. Find the reading of
the ammeter.
conducting loop
0.15 Ω
5 cm
A.
B.
C.
D.
1.00 mA
1.50 mA
2.00 mA
3.00 mA
Answer: A
20
A student passes an alternating current through a long straight wire and uses a search
coil to investigate the variation of the magnitude B of the magnetic field from the wire
with the perpendicular distance r. Which of the following orientation of the search
coil should be used in this investigation?
11
(1)
to CRO
search coil
(2)
to CRO
search coil
(3)
search
coil
to CRO
A.
B.
C.
D.
(1) only
(2) only
(1) and (3) only
(2) and (3) only
Answer: B
21
A bulb is connected to one of the smooth parallel conducting rails in a uniform
magnetic field as shown. A conducting rod PQ is moved to the right at a uniform
speed on the rails.
conducting rail
Q
P
uniform magnetic field
Which of the following statements is/are correct?
(1) The bulb lights up when the rod is moved to the right.
(2) P is at a higher electric potential than Q.
(3) Electric potential energy is supplied by the magnetic force.
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
Answer: B
12