Physics Test

Result

Physics Test - 17

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Question 1
3 / -1

A
1.08 mA

B
0.08 mA

C
1 mA

D
1 A

Solution
Question 2
3 / -1

The thermo-emf of a thermocouple varies with the temperature θ of the hot junction as E = aθ + bθ² in volts ,where the ratio a/b is 700°C. If the cold junction is kept at 0°C, what is the neutral temperature?

A
700°C

B
350°C

C
1400°C

D
No neutral temperature is possible for this thermocouple

Solution

The neutral temperature is the temperature corresponding to maximum thermo-emf.

At neutral temperature \(\frac{\mathrm{d} \mathrm{E}}{\mathrm{d} \theta}=0\)

Here, \(\frac{\mathrm{d} \mathrm{E}}{\mathrm{d} \theta}=0\) implies

\(\mathrm{a}+2 \mathrm{~b} \theta=0\)

on solving,

\(\theta=\frac{-2 \mathrm{~b}}{\mathrm{a}}\)

Given \(\frac{a}{b}=700^{\circ} \mathrm{C}\)

gives \(\theta\)a negative value which is not possible

(Because \(\theta\) is the temperature difference between hot and cold junction which should be positive)
Question 3
3 / -1

If the acceleration due to gravity is 'g' on the surface of Earth, then the value of acceleration due to gravity at a height of 32 km above the surface of Earth is (radius of Earth = 6400 km)

A
0.99g

B
0.8g

C
1.01g

D
0.9g

Solution

The acceleration due to gravity at a height h above the surface of Earth is given by
Question 4
3 / -1

The maximum height attained by a projectile is increased by 10% by increasing its speed of projection, without changing the angle of projection. The percentage increase in the horizontal range will be?

A
20%

B
15%

C
10%

D
5%

Solution
Question 5
3 / -1

If the distance between a point charge and an infinitely large charge plate is increased by factor 2, the new force on the point charge will be

A
decreased by factor 4

B
increased by factor 2

C
decreased by factor 2

D
the same

Solution

Since an infinitely large charged plate will create an uniform field (constant), therefore the force remains the same.
Question 6
3 / -1

Two point charges, each of charge + q, are fixed at (+ a, 0) and (– a, 0). Another positive point charge q placed at the origin is free to move along the x-axis. The charge q at the origin in equilibrium will have

A
maximum force and minimum potential energy

B
minimum force and maximum potential energy

C
maximum force and maximum potential energy

D
minimum force and minimum potential energy

Solution
Question 7
3 / -1

Three rods made of the same material and having the same cross-section have been joined as shown in the figure below. Each rod is of the same length. The left and right ends are kept at 0^oC and 90^oC, respectively. The temperature of the junction of the three rods will be

A
45^oC

B
60^oC

C
30^oC

D
20^oC

Solution
Question 8
3 / -1

A
A + B + C

B

C
0

D
1

Solution
Question 9
3 / -1

The resistance of bulb filament is 100W at a temperature of 100°C. If its temperature coefficient of resistance is 0.005 per °C, its resistance will become 200 W at a temperature (°C) of _____.

A
200

B
100

C
150

D
300

Solution

100 = R₀(1 + 0.005 × 100) -------- (i)

200 = R₀(1 + 0.005 × t) --------- (ii)

Dividing (i) by (ii) and solving

t = 200 °C
Question 10
3 / -1

A liquid takes 6 minutes to cool from 80^oC to 50^oC. If the temperature of the surroundings is 20^oC, then how long will it take to cool from 60^oC to 30^oC?

A
6 minutes

B
8 minutes

C
10 minutes

D
12 minutes

Solution