Engineering Physics Multiple Choice Questions on “Absorption and Emission”.
1. At which temperature, the centigrade and Fahrenheit scales are equally?
a) 40°
b) -40°
c) 37°
d) -80°
Answer: b
Clarification: C/5=(F-32)/9
C/5=(C-32)/9
4C=-160
C=F=-40°.
2. The volume of a gas at 20°C is 100cm3 at normal pressure. If it is heated to 100°C, its volume becomes 125cm3 at the same pressure, then volume coefficients of the gas (at normal pressure) is?
a) 0.0033/°C
b) 0.0025/°C
c) 0.0030/°C
d) 0.0021/°C
Answer: a
Clarification: Vt=V0 (1+γt)
V100/V20 =(1+100γ)/(1+20γ )=125/100=3/4
γ=1/300=0.0033/°C.
3. Density of substance at 0°C is g/cc and 100°C, its density is 9.7g/cc. The coefficient of linear expansion of the substance is?
a) 10-1
b) 10-2
c) 10-3
d) 10-4
Answer: d
Clarification: γ=(ρ0-ρt)/(ρ0×t)=(10-9.7)/(10×100)=3×10-4
α=γ/3=10-4°C-1.
4. The coefficient of volumetric expansion of mercury is 18×10-5/°C. The thermometer bulb has a volume of 10-6 m3 and cross-section of the stem is 0.002cm2. Assuming that bulb is filled with mercury at 0°C, the increase in length of the mercury column at 100°C will be ___________
a) 9cm
b) 9mm
c) 18cm
d) 18mm
Answer: a
Clarification: Let h be the length of mercury column at 100°C. Then
Expansion in mercury = Volume of stem
γV∆T=Ah
h=γV∆T/A=(18×10-5×10-6×100)/(0.002×10-4) m
h=9×10-2 m
h=9cm.
5. Amount of heat required to raise the temperature of a body through 1K is called ___________
a) Specific heat
b) Thermal capacity
c) Water equivalent
d) Entropy
Answer: b
Clarification: The amount of heat required to raise the temperature of a body through 1K is called its thermal capacity.
6. If the temperature of a rod is increased by 10°C, its length increases by 1%. What is the percentage change in volume of the body of the same material for 10°C increase in temperature?
a) 9%
b) 1%
c) 5%
d) 3%
Answer: d
Clarification: ∆I/I×100=100α∆T
∆V/V×100=100γ∆T=100×3α×∆T
Hence for the same rise of temperature, an increase in volume is 3 times the increase in length.
7. In order that the heat flows from one part of a solid to another part, what is required?
a) Uniform density
b) Temperature gradient
c) Density gradient
d) Uniform temperature
Answer: b
Clarification: As heat flows from higher temperature to lower temperature, so a temperature gradient is required.
8. A body A of mass 0.5kg and specific heat 0.85 is at a temperature of 60°C. Another body B of mass 0.3kg and specific heat 0.9 is at a temperature of 90°C. When they are connected to a conducting rod, heat will flow from ___________
a) A to B
b) Heat can’t flow
c) B to A
d) First A to B and then B to A
Answer: c
Clarification: Heat always flows from a body at higher temperature to a body at a lower temperature.
9. Two rods having thermal conductivity in the ratio of 5:3 having equal lengths and equal cross-sectional area are joined end to end. If the temperature of the free end of the first rod is 100°C and free end of the second rod is 20°C, then the temperature of the junction is?
a) 50°C
b) 70°C
c) 60°C
d) 90°C