Physics Test 104

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Physics Test 104

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Weekly Quiz Competition

Question 1
4 / -1

In the circuit shown in figure, determine the voltage V₀ for the circuit network :-

A
11.7 V

B
12 V

C
11.3 V

D
None of these

Solution

In the circuit the direction of conventional current will be same as the arrow head of diodes; hence it may appear that both the diodes are in "on" state. Voltage drop across the silicon diode is 0.7V and germanium diode is 0.3V. In a parallel branches potential difference across each branch must be same. Here 0.7V drop across silicon diode does not match that of 0.3V across germanium diode. This complexity is voltage increases form 0 to 12V in a time of the order of millisecond. As soon as the voltage across the germanium diode reaches 0.3V, it is in "on" stage and it maintains a level of 0.3V. The voltage drop across silicon diode never reaches 0.7V; hence it remains in its open circuit state. The resulting circuit is shown in figure.

V₀ = 12 – 0.3 = 11.7 V
Question 2
4 / -1

Two point charges q and –q are at positions(0, 0, d) and (0, 0, –d) respectively. What is the electric field at (a, 0, 0)?

A

B

C

D

Solution
Question 3
4 / -1

Six equal capacitors each of capacitance C are connected as shown in the figure. Then the equivalent capacitance between A and B is :-

A
6C

B
C

C
2C

D
C/2

Solution

The given network of capacitors can be redrawn as follows :

C₄ is in parallel to a balanced Wheatstone bridge made from the rest five capacitors as shown in the figure. Therefore, equivalent capacitance = C + C = 2C
Question 4
4 / -1

A battery has an emf of 15 V and internal resistance of 1Ω. Is the terminal to terminal potential difference less than, equal to or greater than 15 V if the current in the battery is: (i) from negative to positive terminal, (ii) from positive to negative terminal (iii) zero current?

A
Less, Greater, Equal

B
Less, Less, Equal

C
Greater, Greater, Equal

D
Greater, Less, Equal

Solution

(i) v = ε – ir

(ii) v = ε + ir

(iii) v = ε
Question 5
4 / -1

Find magnetic moment of a disc with uniform charge distribution 'q' and radius R when rotated about its diameter with angular velocity

A
qR²w / 8

B
qR²w / 4

C
qR²w / 2

D
qR²w

Solution
Question 6
4 / -1

The current in the given circuit is increasing with a rate 4 amp/s. The charge on the capacitor at an instant when the current in the circuit is 2 amp will be :

A
4μC

B
5μC

C
6μC

D
none of these

Solution
Question 7
4 / -1

In an A.C. circuit, the instantaneous e.m.f. and current are given by

e = 100 sin 30 t

i = 20 sin (30t - π/4)

In one cycle of A.C. the average power consumed by the circuit and the wattless current are, respectively.

A
100 / √2, 10

B
50 / √2, 0

C
50, 0

D
50, 10

Solution

P_av = , wattles current = i_rms sinϕ
Question 8
4 / -1

A person is in a room whose ceiling and two adjacent walls are plane mirrors. How many images are formed :-

A
5

B
6

C
7

D
8

Solution

The walls acts as two mirror inclined to each other at 90° and so they will form 3 images of the person. Now these images and person will act as object for the ceiling mirror and ceiling mirror will form 4 images. Therefore total number of images formed = 3 + 4 = 7
Question 9
4 / -1

To an observer on the earth, the stars appear to twinkle. This can be described by :-

A
The fact that stars do not emit light continuously

B
Frequency absorption of star light by their own atmosphere

C
Frequency absorption of star light by the earth's atmosphere

D
The refractive index fluctuations in the earth's atmosphere

Solution

Stars appear to twinkle due to fluctuations of refractive index of earth's atmosphere.
Question 10
4 / -1

A diverging beam of light from a point source S having divergence angle α, falls symmetrically on a glass slab as shown. The angles of incidence of the two extreme rays are equal. If the thickness of the glass slab is t and the refractive index n, then the divergence angle of the emergent beam is

A
zero

B
α

C
sin^–1(1/n)

D
2sin^–1(1/n)

Solution

Glass slab produces zero deviation, so angle of divergence does not change.