Physics Test 127

Result

Physics Test 127

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Weekly Quiz Competition

Question 1
4 / -1

The antenna current of an AM transmitter is 8 A when only carrier wave is sent but the current increases to 8.88 A when the carrier wave is sinusoidally modulated. The percentage of modulation is

A
62%

B
65%

C
68%

D
71%

Solution
Question 2
4 / -1

A square metal wire loop of side 20 cm and resistance 1 Ω is moved with a constant velocity Vo in a uniform magnetic field of induction B = 4 Wb/m². The magnetic field lines are perpendicular to the plane of the loop and directed inwards. The loop is connected to a network of resistors each of value 2 Ω . The resistance of load wires AB and CD are negligible. To get a current of 2 mA in the loop, the speed of motion of the loop is

A
0.55 cm/s

B
0.65cm/s

C
0.75 cm/s

D
0.85 cm/s

Solution

The network of resistors in a balanced Wheatstone's network. Hence the resistance EF is ineffective. The equivalent resistance R' of the network is

The resistance of the square loop is 1 Ω
∴ effective resistance of the circuit R = 2 + 1 = 3 Ω
Question 3
4 / -1

Four identical hollow cylindrical columns of steel, support a big structure of mass 60,000 kg. The inner and outer radii of each column are 40 cm and 50 cm respectively. When the load distribution is uniform, the compressional strain on each column is (Young’s modulus of steel is 2 x 10¹¹ Pa)

A
2.65 x 10^-6

B
2.45 x 10^-6

C
2.45 x 10^-4

D
2.65 x 10^-4

Solution

Total mass supported by the columns = 60,000 kg
Total weight supporte d = 60,000 x 10 N

Compressional force one achcolumn ,

Cross-sectional area of each colum n,
Question 4
4 / -1

A steel ball of mass 60 g falls from a height 0.8 m on the horizontal surface of a massive slab. The coefficient of restitution between the ball and the slab is e = 0.4; the total momentum imparted to the slab by the ball after numerous bounces is

A
0.56 Ns

B
0.64 Ns

C
0.72 Ns

D
0.78 Ns

Solution

By Newton’s law of collision, the velocity v′ after the first impact is v′ = ev (upward direction).
Question 5
4 / -1

In nuclear reaction, energy released per fission is 200 MeV. When uranium 235 is used as nuclear fuel in a reactor having a power level of 1 MW, the amount of fuel needed in 30 days will be

A
48 g

B
42 g

C
38 g

D
32 g

Solution

Energy produced by the reactor in 1 day = 10⁶ x 86400 J
Energy released per fission = 200 x 10⁶ x 1.6 x 10^-19 J
No. of fissions required (i.e.,) no. of ²³⁵U atoms fissioned in a month
Question 6
4 / -1

The temperature at which the speed of sound in oxygen will be same as the speed of sound in nitrogen at 25 °C-

A
61.7 °C

B
63.5 °C

C
65.4 °C

D
67.6 °C

Solution
Question 7
4 / -1

An alternating voltage having frequency of 50 cycles/sec and maximum voltage 220 V is supplied to a circuit containing a pure inductance of 0.02 H and a pure resistance of 10 Ω in series. The value of maximum current in circuit is-

A
16.52 A

B
18.64 A

C
20.18 A

D
22. 73 A

Solution
Question 8
4 / -1

A beam of light traveling in water strikes a glass plate which is also immersed in water. When the angle of incidence is 50 ° the reflected beam is found to be plane polarised. The refractive index of water is 4/3. The refractive index of the glass plate is (Given tan 50 ° = 1.198)

A
1.54

B
1.57

C
1.60

D
1.63

Solution
Question 9
4 / -1

A reversible heat engine converts one fourth of heat input into work. When the temperature of the sink is reduced by 200 K, its efficiency is doubled. The temperature of the source is

A
800 K

B
750 K

C
700 K

D
650 K

Solution
Question 10
4 / -1

A man pulls a loaded sledge of mass 60 kg along a horizontal surface at constant velocity as shown in figure. The coefficient of kinetic friction between the sledge and the surface is 0.15. The tension in the rope during pulling when it makes an angle of cp = 40 ° with the horizontal is (cos 40 0 = 0.766, sin 40 ° = 0.643 and g = 10 ms'2)

A
102.6 N

B
104.4 N

C
106.7 N

D
108.3 N

Solution

Free body diagram