Transmission of Heat - CBSE STD 12 Science JEE physics Questions

Q 1Assertion & Reason1 Mark

Assertion : For higher temperature, the peak emission wavelength of a black body shifts to lower wavelengths.
Reason : Peak emission wavelength of a blackbody is proportional to the fourth power of temperature.

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Q 2Assertion & Reason1 Mark

Assertion : A body that is a good radiator is also a good absorber of radiation at a given wavelength.
Reason : According to Kirchoff's law the absorptivity of a body is equal to its emissivity at a given wavelength.

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Q 3Assertion & Reason1 Mark

Assertion : Bodies radiate heat at all temperatures.
Reason : Rate of radiation of heat is proportional to the fourth power of absolute temperature.

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Q 4Assertion & Reason1 Mark

Assertion : The radiation from the sun's surface varies as the fourth power of its absolute temperature.
Reason : The sun is not a black body.

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Q 5Assertion & Reason1 Mark

Assertion : The equivalent thermal conductivity of two plates of same thickness in contact (series) is less than the smaller value of thermal conductivity.
Reason : For two plates of equal thickness in contact (series) the equivalent thermal conductivity is given by

\frac{1}{K}=\frac{1}{K_1}+\frac{1}{K_2}

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Q 6MCQ1 Mark

The radiation energy density per unit wavelength at a temperature $T$ has a maximum at a wavelength $\lambda$. At temperature $2 T$, it will have a maximum at a wavelength

A
$4 \lambda$
B
$2 \lambda$
✓
$\lambda / 2$
D
$\lambda / 4$

Answer: C.

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Q 7MCQ1 Mark

The total energy radiated from a black body source is collected for one minute and is used to heat a quantity of water. The temperature of water is found to increase form $20^{\circ} \mathrm{C}$ to $20.5^{\circ} \mathrm{C}$. If the absolute temperature of the black body is doubled and the experiment is repeated with the same quantity of water at $20^{\circ} \mathrm{C}$, the temperature of water will be

A
$21^{\circ} \mathrm{C}$
B
$22^{\circ} \mathrm{C}$
C
$24^{\circ} \mathrm{C}$
✓
$28^{\circ} \mathrm{C}$

Answer: D.

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Q 8MCQ1 Mark

Solar radiation emitted by sun resembles that emitted by a black body at a temperature of $6000 \mathrm{~K}$. Maximum intensity is emitted at a wavelength of about $4800 \mathring A$. If the sun were to cool down from $6000 K$ to $3000 K$ then the peak intensity would occur at a wavelength

A
$4800 \mathring A$
✓
$9600 \mathring A$
C
$7200 \mathring A$
D
$6400 \mathring A$

Answer: B.

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Q 9MCQ1 Mark

Three rods of the same dimension have thermal conductivities $3 K, 2 K$ and $K$. They are arranged as shown in fig. Given below, with their ends at $100 C, 50 C$ and $20 C$. The temperature of their junction is

A
$60^{\circ} \mathrm{C}$
✓
$70^{\circ} \mathrm{C}$
C
$50 \mathrm{C}$
D
$35 C$

Answer: B.

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Q 10MCQ1 Mark

Two rods (one semi-circular and other straight) of same material and of same cross-sectional area are joined as shown in the figure. The points $A$ and $B$ are maintained at different temperature. The ratio of the heat transferred through a cross-section of a semicircular rod to the heat transferred through a cross section of the straight rod in a given time is

✓
$2: \pi$
B
$1: 2$
C
$\pi: 2$
D
$3: 2$

Answer: A.

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Transmission of Heat question types

Transmission of Heat questions

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Transmission of Heat JEE physics - Transmission of Heat

Transmission of Heat question types

Transmission of Heat questions

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