**31. **The temperature gradient across a copper rod of thickness 0.02m, maintained at two temperature junctions of 20º and 80ºC respectively is?

**A.**3.0 x 10^{2}km^{−1}**B.**3.0 x 10^{3}km^{−1}**C.**5.0 x 10^{3}km^{−1}**D.**3.0 x 10^{4}km^{−1}

**Correct Option: Answer is B**

**32. **Calculate the mass of ice that would melt when 2kg of copper is quickly transferred from boiling water to a block of ice without heat loss (specific heat capacity of copper = 400Jkg^{1}k^{−1}, latent heat of fusion of ice = 3.3 x 10^{5}Jkg^{−1})

**A.**8/3.3kg**B.**3.3/80kg**C.**80/33kg**D.**3.3/8kg

**Correct Option: Answer is A**

**33. **The equation of a wave traveling along the positive x-direction is given by; y = 0.25 x 10 – 3 sin (500πt – 0.025x). Determine the angular frequency of the wave motion.

**A.**0.25 x 10^{−3}rads^{−1}**B.**0.25 x 10^{−1}rads^{−1}**C.**5.00 x 10^{2}rads^{−1}**D.**2.50 x 10^{3}rads^{−1}

**Correct Option: Answer is C**

Using y = A sin (wt + 0)

Given y = 0.25 x 10^{−3}sin (500t – 0.025x)

By comparing, w = 5.00 x 10^{2}rads^{−1}

**34. **If a sound wave goes from a cold air region to a hot air region, its wavelength will——

**A.**increase**B.**decrease**C.**decrease then increase**D.**remain constant

**Correct Option: Answer is A**

**35. **The lowest note emitted by a stretched string has a frequency of 40Hz. How many overtones are there between 40Hz and 180Hz?

**A.**4**B.**3**C.**2**D.**1

**Correct Option: Answer is B**

f^{0}0 = 40H^{3}

1st overtone = 2f^{0} = 80H^{3}

2nd overtone = 3f^{0} = 120H^{3}

3rd overtone = 4f^{0} = 160H^{3}

4th overtone = 5f^{0} = 200H^{3}

∴ Number of overtones between 40H^{3} and 180H^{3} = 3

**36. **A man stands 4m in front of a plane mirror. If the mirror is moved 1m towards the man, the distance between him and his new image is—–

**A.**3m**B.**5m**C.**6m**D.**10m

**Correct Option: Answer is C**

Objects distance (u) = image distance (v)

object distance = 3m

|uv| = 3 + 3 = 6m

**37. **The inside portion of part of a hollow metal sphere of diameter 20cm is polished. The portion will therefore form a

**A.**concave mirror of focal length 5cm**B.**concave mirror of focal length 10cm**C.**convex mirror of focal length 5cm**D.**convex mirror of focal length 10cm

**Correct Option: Answer is A**

**38. **The velocities of light in air and glass are 3.0 x 108ms^{−1}and 2.0 x 108ms^{−1} If the angle of refraction is 30º, the sine of the angle of incidence is

**A.**0.33**B.**0.50**C.**0.67**D.**0.75

**Correct Option: Answer is D**

**39. **An astronomical telescope is said to be in normal adjustment when the——

**A.**eye is accommodated**B.**focal length of an object lens is longer than that of eye piece**C.**final image is at the near point of eye**D.**final image is at infinity

**Correct Option: Answer is D**

**40. **A 2H inductor has negligible resistance and is connected to a 50πHz A.C supply. The reactance of the inductor is?

**A.**200Ω**A.**50Ω**C.**100/π**D.**25/Πω