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Free download in PDF CBSE Class 12 Physics MCQs with Answers. Here Gkseries provide Physics Solve Questions and Answers for CBSE Class 12 Students.
101
When the rate of change oic current is unity, the induced emf is equal to
[A]
thickness of coil
[B]
number of turns in coil
[C]
coefficient of self inductance
[D]
total flux linked with coil
Answer: coefficient of self inductance
102
Two inductors of inductance .L each are connected in series with opposite? magnetic fluxes. The resultant inductance is
(Ignore mutual inductance)
[A]
zero
[B]
L
[C]
2L
[D]
3L
103
The phase difference between the alternating current and emf is TE/2. Which ofthe following cannot be the constituent of the circuit?
[A]
C alone
[B]
L alone
[C]
L and C
[D]
R and L
104
In an LCR-series ac circuit, the voltage across each of the component L, C and R is 50 V. The voltage across the LC-combination will be
[A]
50 V
[B]
50√2 V
[C]
100 V
[D]
zero
105
In an LCR circuit, capacitance is charged from C to 2C. For resonant frequency to remain unchanged, the inductance should be changed from L to
[A]
4 L
[B]
2 L
[C]
L/2
[D]
L/4
106
The core of any transformer is laminated so as to
[A]
reduce the energy loss due to eddy currents.
[B]
make it light weight.
[C]
make it robust and strong.
[D]
increase the secondary voltage.
Answer: reduce the energy loss due to eddy currents.
107
If coil is open, then L and R becomes
[A]
infinity, zero
[B]
zero, infinity
[C]
infinity, infinity.
[D]
zero, zero
108
Which quantity is increased in a step-down transformer?
[A]
Frequency
[B]
Current
[C]
Voltage
[D]
Power
109
If an AC voltage is applied to an ICi? circuit, which of the following is true?
[A]
I and V are out of phase with each other inR.
[B]
I and V are in phase in L while in C, they are out of phase.
[C]
I and V are out of phase in both C and L.
[D]
I and V are out of phase in L and in phase in C.
Answer: I and V are out of phase in both C and L.
110
The peak value of ac voltage on a 220 V mains is
[A]
200√2 V
[B]
230√2 V
[C]
220√2 V
[D]
240√2 V
111
A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
[A]
30%
[B]
50%
[C]
90%
[D]
10%
112
Choose the correct statement.
[A]
A capacitor can conduct a dc circuit but not an inductor.
[B]
In a dc circuit the inductor can conduct but not a capacitor.
[C]
In dc circuit both the inductor and capacitor cannot conduct.
[D]
The inductor has infinite resistance in a dc circuit.
Answer: In a dc circuit the inductor can conduct but not a capacitor.
113
A coil of self-inductance L is connected in series with a bulb B and an ac source. Brightness of the bulb decreases when
[A]
frequency of the ac source is decreased.
[B]
number of turns in the coil is reduced.
[C]
a capacitance of reactance Xc = XL in included.
[D]
an iron rod is inserted in the coil.
Answer: an iron rod is inserted in the coil.
114
In the formation of a rainbow, the light from the sun on water droplets undergoes
[A]
dispersion only.
[B]
only TIR.
[C]
dispersion and TIR.
[D]
scattering.
115
If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power?
[A]
+ 6.5 D
[B]
– 6.5 D
[C]
+ 7.5 D
[D]
– 0.75 D
116
Air bubble in water behaves as
[A]
sometimes concave, sometimes convex lens
[B]
concave lens
[C]
convex lens
[D]
always refracting surface
117
In optical fibres, the refractive index of the core is
[A]
greater than that of the cladding.
[B]
equal to that of the cladding.
[C]
smaller than that of the cladding.
[D]
independent of that of cladding.
Answer: greater than that of the cladding.
118
A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen.
[A]
half the image will disappear.
[B]
incomplete image will be formed.
[C]
intensity of image will decrease but complete image is formed.
[D]
intensity of image will increase but image is not distinct.
Answer: intensity of image will decrease but complete image is formed.
119
Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is , [NCERT Exemplar]
[A]
36 × 10-5 kg m/s.
[B]
36 × 10-4 kg m/s.
[C]
108 × 104 kgm/s.
[D]
1.08 × 107 kg m/s.
Answer: 36 × 10-4 kg m/s.
120
Which of the following electromagnetic waves is used in medicine to destroy cancer cells?
[A]
IR-rays
[B]
Visible rays
[C]
Gamma rays
[D]
Ultraviolet rays
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