This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Absorption and Emission”.
1. At which temperature, the centigrade and Fahrenheit scales are equally?
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
Explanation: Vt=V0 (1+γt)
V100/V20 =(1+100γ)/(1+20γ )=125/100=3/4
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
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
Explanation: Let h be the length of mercury column at 100°C. Then
Expansion in mercury = Volume of stem
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
Explanation: 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?
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
Explanation: 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
Explanation: 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
Explanation: Let T be the temperature of the junction. In the steady state,
(K1 A(100-T))/d=(K2 A(T-T2))/d
8T=560 or T=70°C.
10. Mud houses are cooler in summer and warmer in winter because
a) Mud is a good conductor of heat
b) Mud is a superconductor of heat
c) Mud is a bad conductor of heat
d) Mud can adapt according to temperature
Explanation: Mud is an ad conductor of heat. It does not allow heat to come in from outside in summer and it does not allow heat to go out from a house in winter.
11. A perfectly black body is one whose
a) Absorptive power is 1
b) Absorptive power is 0
c) Emissive power is 1
d) Absorptive power is 0.5
Explanation: A black body is one which absorbs the entire radiation incident upon it. Its absorptive power is unity.
12. A black body radiates energy at the rate of 1×105 J/(sm)2 at a temperature of 227°C. The temperature to which it must be heated so that it radiates energy at the rate of 1×109 J/(sm)2
a) 5000 K
c) 500 K
Explanation: From Stefan’s law,
13. A black body at 200 K is found to emit maximum energy at a wavelength 14μm. When its temperature is raised to 1000K, then wavelength at which maximum energy emitted it
Explanation: By Wien’s law,
14. The triple point of water is
Explanation: Triple point of water corresponds to a temperature of 273.16K and a pressure of 0.46cm of Hg.
15. During constant temperature, we feel colder on the day when the humidity is
Explanation: If relative humidity is low, we feel colder because of rapid evaporation of sweat from our body.
Sanfoundry Global Education & Learning Series – Engineering Physics.
To practice all areas of Engineering Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.