Physics Test 298

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Physics Test 298

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Weekly Quiz Competition

Question 1
4 / -1

In a capillary tube of radius 'R', a straight thin metal wire of radius 'r' (R > r) is inserted symmetrically and one end of the combination is dipped vertically in water such that the lower end of the combination is at same level. The rise of water in the capillary tube is [T = surface tension of water, ρ = density of water, g = gravitational acceleration]

A

B

C

D

Solution
Question 2
4 / -1

Three magnetic materials are listed below

(A) paramagnetics

(B) diamagnetics

(C) ferromagnetics

Choose the correct order of the materials in increasingorder of magnetic susceptibility.

A
(A), (B), (C)

B
(C), (A), (B)

C
(B), (A), (C)

D
(B), (C), (A)
Solution
The given magnetic materials are:
- (A) Paramagnetics
- (B) Diamagnetics
- (C) Ferromagnetics
In increasing order of magnetic susceptibility:

Diamagnetics (B) < Paramagnetics (A) < Ferromagnetics (C)

The correct option is (3).
Question 3
4 / -1

Two wires A and B are of the same materials. Their lengths are in the ratio 1 : 2 and the diameters are in the ratio 2 : 1, When stretched by force F_A and F_B respectively they get equal increase in their lengths. Then the ratio should be:

A
1 : 2

B
1 : 1

C
2 : 1

D
8 : 1

Solution
Question 4
4 / -1

A wire of length ‘l’ and resistance 100 Ω is divided into 10 equal parts. The first 5 parts are connected in series while the next 5 parts are connected in parallel. The two combinations are again connected in series. The resistance of this final combination is:

A
26 Ω

B
52 Ω

C
55 Ω

D
60 Ω

Solution

Wire resistance = 100 Ω

Divide into 10 equal parts

so each part resistance r = (100 / 10 ) + 10 Ω

R_eq= 5 × 10 +(10/5)

R_eq = 52

The correct answer is option 2.
Question 5
4 / -1

Two small spherical metal balls, having equal masses, are made from materials of densities ρ₁ and ρ₂ (ρ₁ = 8ρ₂) and have radii of 1 mm and 2 mm, respectively, They are made to fall vertically (from rest) in a viscous medium whose coefficient of viscosity equals η and whose density is 0.1 ρ₂. The ratio of their terminal velocities would be,

A

B

C

D

Solution
Question 6
4 / -1

An ac source is connected to a capacitor C. Due to decrease in its operating frequency:

A
capacitive reactance decreases.

B
displacement current increases.

C
displacement current decreases.

D
capacitive reactance remains constant

Solution

The Correct answer is option 3.

Key Points
Question 7
4 / -1

Light travels a distance x in time t₁ in air and 10x in time t₂ in another denser medium. What is the critical angle for this medium?

A

B

C

D

Solution

Speed of light in air = V₁ = x/t₁

Speed of light in medium = V₂ = 10x/t₂

Sin θ = V₂/V₁

Sinθ = 10x/t₂× t₁/x

θ = Sin^-1(10t₁/t₂)

∴ The correct option is 4)
Question 8
4 / -1

Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de-Broglie wavelength associated with the electrons would

A
Increase by 4 times

B
Increase by 2 times

C
Decrease by 2 times

D
Decrease by 4 times

Solution

When the voltage was increased from 25Kv to 100 Kv then the de-Broglie wavelength associated with the electrons would decrease by 2 times. Therefore option 3 is correct.
Question 9
4 / -1

The two ends of a long cylinder containing gas are maintained at different temperatures. Which of the following quantities will have the same value throughout the cylinder?

A
Pressure

B
Density

C
The ratio of pressure to density

D
The number of molecules per unit volume

Solution

Temperature: The temperature will vary along the length of the cylinder because the ends are maintained at different temperatures.

This creates a temperature gradient.

Density: The density of the gas may also vary along the length of the cylinder because temperature affects the density.

A higher temperature can cause the gas to expand, reducing its density, and vice versa.

Pressure: In a cylinder containing gas, if it is in a steady state and no external forces (like gravity) are acting on it, the pressure typically remains constant throughout the cylinder.

This is because any pressure difference would cause the gas to move and equalize the pressure throughout the system.

Molar concentration: This might change with temperature, as temperature can affect how the molecules are distributed in the gas.

∴ The correct option is 1
Question 10
4 / -1

Addition of trivalent impurity to a pure semiconductor creates many

A
free electrons

B
valence electrons

C
holes

D
bound electrons
Solution
- When a trivalent impurity (an element with three valence electrons, such as boron) is added to a pure semiconductor (like silicon), it results in the formation of "holes" in the crystal structure.
- Trivalent atoms have one less electron than needed to complete the bonding with neighboring silicon atoms.
- This missing electron creates a "hole," which acts as a positive charge carrier in the material. Thus, the addition of a trivalent impurity leads to a p-type semiconductor with holes as the majority charge carriers.