The graph shows the variation with time t of the
magnetic flux φ through a coil that is rotating in a
uniform magnetic field. The magnitude of the emf
induced across the ends of the coil is maximum at
time(s)
A.
B.
C.
D.
t1 and t3.
t2 and t4.
t3 only.
t4 only.
Two forces of magnitudes 7 N and 5 N act
at a point. Which one of the following is
not a possible value for the magnitude of
the resultant force?
A.
B.
C.
D.
1N
3N
5N
7N
A coil is rotated at constant speed in a region of uniform
magnetic field. The graph shows the variation with time t of
the emf ε induced in the coil for one cycle of rotation.
At what time(s) is the flux linkage in the coil a maximum?
5 or 15 ms
A coil is rotated at constant speed in a region of uniform
magnetic field. The graph shows the variation with time t of
the emf ε induced in the coil for one cycle of rotation.
Determine the rate of change of flux at t = 4.0 ms.
2.0 V / Wb s-1
A coil is rotated at constant speed in a region of uniform
magnetic field. The graph shows the variation with time t of
the emf ε induced in the coil for one cycle of rotation.
Calculate the root mean square value of the induced emf.
4.2 V
The ratio
is approximately equal to
A.
B.
C.
D.
10–15.
10–8.
10–5.
–2
10 .
A magnetic flux linking a wire loop changes
sinusoidally with time. The emf induced in the
loop changes sinusoidally
A. in phase with the changing flux.
B. out of phase with the changing flux by a
quarter period.
C. out of phase with the changing flux by a
third of a period.
D. out of phase with the changing flux by
half a period.
The maximum output voltage of a generator
is V0. The frequency of rotation of the
generator coil is doubled. What is the new
maximum output voltage?
A.
B.
C.
D.
V0
V0
2V0
4 V0
The diagram below shows an ideal transformer.
laminated core
primary coil
secondary coil
The primary coil of an ideal transformer is connected to an
alternating supply rated at 230V. The transformer is designed to
provide power for a lamp rated as 12V, 42W and has 450 turns of
wire on its secondary coil.
8600 turns, 180 mA
Determine the number of turns of wire on the primary coil and the
current from the supply for the lamp to operate at normal
brightness.
The magnetic flux Φ through a coil having 500
turns varies with time t as shown below.
The magnitude of the emf
induced in the coil is
A.
B.
C.
D.
0.25 V.
0.50 V.
250 V.
1 000 V.
An alternating supply of constant r.m.s. current and
constant r.m.s. potential difference is connected to the
primary coil of an ideal transformer. Which one of the
following describes the effect, if any, on the r.m.s. current
and on the r.m.s. power in the circuit of the secondary coil
when the number of turns on the secondary coil is
increased?
A.
B.
C.
D.
r.m.s. current
no change
no change
Decreases
Decreases
r.m.s. power
increases
no change
increases
no change