Mechanical Engineering MCQs [Quiz 41]

Q1. The thermal diffusivities for solids are generally
(a) less than those for gases
(b) jess than those for liquids
(c) more than those for liquids and gases
(d) more or less same as for liquids and gases
(e) zerci.

Q2. Thermal diffusivity of a substance is
(a) directly proportional to thermal con¬ductivity
(b) inversely proportional to density of substance
(c) inversely proportional to specific heat
(d) all of the above
(e) none of the above.

Q3. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
(a) Krichoff’s law
(b) Stefan’s law
(c) Wien’ law
(d) Planck’s law
(e) Black body law.

Q4. According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to
(a) absolute temperature
(b) T2
(c) T5
(d) t
(e) l/T.

Q5. According to Wien’s law, the wavelength corresponding to maximum energy is proportion to
(a) absolute temperature (T)
(b) I2
(c) f
(d) t
(e) 1/r.

Q6. Depending on the radiating properties, a body will be white when
(a) p = 0, x = 0 and a = 1
(b) p=l,T = 0anda = 0
(c) p = 0, x = 1 and a = 0
(d) x = 0, a + p = 1
(e) a = 0, x + p = 1.
where a = absorptivity, p = reflectivity, x = transmissivity

Q7. Depending on the radiating properties, a body will be black when
(a) p = 0, x = 0 and a = 1
(b) p= l,T = 0anda = 0
(c) p = 0, x = 1 and a = 0
(d) x = 0, a + p = 0
(e) a = 0,x + p= 1.
where a = absorptivity, p == reflectivity, X = transmissivity.

Q8. Depending on the radiating properties, a body will be opaque when
(a) p = 0, x = 0 and a = 1
(b) p=l,x = 0anda = 0
(c) p = 0, x = 1 and a = 0
(d) x – 0, a + p = 1
(e) a=0,x + p= 1.
where a = absorptivity, p = reflectivity, X = transmissivity

Q9. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
(a) temperature
(b) thickness
(c) area
(d) time
(e) area and time.

Q10. The ratio of the energy absorbed by the body to total energy falling on it is called
(a) absorptive power
(b) emissive power
(c) absorptivity
(d) emissivity
(e) none of the above.

Updated: 27th August 2019 — 9:11 PM

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