QBManager

Heat Transfer

149599 The tungsten filament of an electric lamp has a surface area $A$ and a power rating $P$ . If the emissivity of the filament is $\in$ and $σ$ is Stefan's constant, the steady temperature of the filament will be

1

T = {(\frac{P}{A \in σ})}^{4}

2

T = (\frac{P}{A \in σ})

3

T = {(\frac{A \in σ}{P})}^{\frac{1}{4}}

4

T = {(\frac{P}{A \in σ})}^{\frac{1}{4}}

Explanation:

D Radiant power $P$ is defined as energy radiated per unit area $i e$
$P = A \in σ T^{4}$
$T = {(\frac{P}{A \in σ})}^{1 / 4}$

MP PMT-2009

Heat Transfer

149607 Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. First and third plates are maintained at absolute temperatures $2 T$ and $3 T$ respectively.
Temperature of the middle plate in steady state is $s$

1

{(\frac{65}{2})}^{\frac{1}{4}} T

2

{(\frac{97}{4})}^{\frac{1}{4}} T

3

{(\frac{97}{2})}^{\frac{1}{4}} T

4

(97)^{\frac{1}{4}} T

Explanation:

C Let $T^{'}$ be the temperature of middle plate. In steady state, energy absorbed by middle plate is equal to energy released by middle plate.
$σ A [(3 T)^{4} - {(T^{'})}^{4}] = σ A [{(T^{'})}^{4} - (2 T)^{4}]$
$2 {(T^{'})}^{4} = 97 T^{4}$
$T^{'} = {(\frac{97}{2})}^{1 / 4} T$

AP EAMCET (22.04.2018) Shift-1

Heat Transfer

149591 Evening Sun is not as hot as the mid day sun. What is the reason?

1 In the evening radiations travel slowly

2 In the evening the temperature of the sun decreases

3 Ozone in atmosphere absorbs more light in the evening

4 In the evening radiations travel a long distance through atmosphere

NDA (I) 2008

Heat Transfer

149443 For any material, if $R, T$ and $A$ represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true

1

R = 1, T = 0, A = 0

2

R = 1, T = 1, A = 0

3

R = 0, T = 1, A = 1

4

R = 0, T = 0, A = 1

5

R = 0, T = 1, A = 0

Explanation:

D We know the relation between $R, T$ and $A$ is $A + T + R = 1$ (i)
for ideal black body, reflection co-efficient and transparent co-efficient is zero then from equation (i) $R = 0, T = 0, A = 1$

Kerala CEE -2018

Heat Transfer

149599 The tungsten filament of an electric lamp has a surface area $A$ and a power rating $P$ . If the emissivity of the filament is $\in$ and $σ$ is Stefan's constant, the steady temperature of the filament will be

1

T = {(\frac{P}{A \in σ})}^{4}

2

T = (\frac{P}{A \in σ})

3

T = {(\frac{A \in σ}{P})}^{\frac{1}{4}}

4

T = {(\frac{P}{A \in σ})}^{\frac{1}{4}}

Explanation:

D Radiant power $P$ is defined as energy radiated per unit area $i e$
$P = A \in σ T^{4}$
$T = {(\frac{P}{A \in σ})}^{1 / 4}$

MP PMT-2009

Heat Transfer

149607 Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. First and third plates are maintained at absolute temperatures $2 T$ and $3 T$ respectively.
Temperature of the middle plate in steady state is $s$

1

{(\frac{65}{2})}^{\frac{1}{4}} T

2

{(\frac{97}{4})}^{\frac{1}{4}} T

3

{(\frac{97}{2})}^{\frac{1}{4}} T

4

(97)^{\frac{1}{4}} T

Explanation:

C Let $T^{'}$ be the temperature of middle plate. In steady state, energy absorbed by middle plate is equal to energy released by middle plate.
$σ A [(3 T)^{4} - {(T^{'})}^{4}] = σ A [{(T^{'})}^{4} - (2 T)^{4}]$
$2 {(T^{'})}^{4} = 97 T^{4}$
$T^{'} = {(\frac{97}{2})}^{1 / 4} T$

AP EAMCET (22.04.2018) Shift-1

Heat Transfer

149591 Evening Sun is not as hot as the mid day sun. What is the reason?

1 In the evening radiations travel slowly

2 In the evening the temperature of the sun decreases

3 Ozone in atmosphere absorbs more light in the evening

4 In the evening radiations travel a long distance through atmosphere

NDA (I) 2008

Heat Transfer

149443 For any material, if $R, T$ and $A$ represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true

1

R = 1, T = 0, A = 0

2

R = 1, T = 1, A = 0

3

R = 0, T = 1, A = 1

4

R = 0, T = 0, A = 1

5

R = 0, T = 1, A = 0

Explanation:

D We know the relation between $R, T$ and $A$ is $A + T + R = 1$ (i)
for ideal black body, reflection co-efficient and transparent co-efficient is zero then from equation (i) $R = 0, T = 0, A = 1$

Kerala CEE -2018

Heat Transfer

149599 The tungsten filament of an electric lamp has a surface area $A$ and a power rating $P$ . If the emissivity of the filament is $\in$ and $σ$ is Stefan's constant, the steady temperature of the filament will be

1

T = {(\frac{P}{A \in σ})}^{4}

2

T = (\frac{P}{A \in σ})

3

T = {(\frac{A \in σ}{P})}^{\frac{1}{4}}

4

T = {(\frac{P}{A \in σ})}^{\frac{1}{4}}

Explanation:

D Radiant power $P$ is defined as energy radiated per unit area $i e$
$P = A \in σ T^{4}$
$T = {(\frac{P}{A \in σ})}^{1 / 4}$

MP PMT-2009

Heat Transfer

149607 Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. First and third plates are maintained at absolute temperatures $2 T$ and $3 T$ respectively.
Temperature of the middle plate in steady state is $s$

1

{(\frac{65}{2})}^{\frac{1}{4}} T

2

{(\frac{97}{4})}^{\frac{1}{4}} T

3

{(\frac{97}{2})}^{\frac{1}{4}} T

4

(97)^{\frac{1}{4}} T

Explanation:

C Let $T^{'}$ be the temperature of middle plate. In steady state, energy absorbed by middle plate is equal to energy released by middle plate.
$σ A [(3 T)^{4} - {(T^{'})}^{4}] = σ A [{(T^{'})}^{4} - (2 T)^{4}]$
$2 {(T^{'})}^{4} = 97 T^{4}$
$T^{'} = {(\frac{97}{2})}^{1 / 4} T$

AP EAMCET (22.04.2018) Shift-1

Heat Transfer

149591 Evening Sun is not as hot as the mid day sun. What is the reason?

1 In the evening radiations travel slowly

2 In the evening the temperature of the sun decreases

3 Ozone in atmosphere absorbs more light in the evening

4 In the evening radiations travel a long distance through atmosphere

NDA (I) 2008

Heat Transfer

149443 For any material, if $R, T$ and $A$ represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true

1

R = 1, T = 0, A = 0

2

R = 1, T = 1, A = 0

3

R = 0, T = 1, A = 1

4

R = 0, T = 0, A = 1

5

R = 0, T = 1, A = 0

Explanation:

D We know the relation between $R, T$ and $A$ is $A + T + R = 1$ (i)
for ideal black body, reflection co-efficient and transparent co-efficient is zero then from equation (i) $R = 0, T = 0, A = 1$

Kerala CEE -2018

Heat Transfer

149599 The tungsten filament of an electric lamp has a surface area $A$ and a power rating $P$ . If the emissivity of the filament is $\in$ and $σ$ is Stefan's constant, the steady temperature of the filament will be

1

T = {(\frac{P}{A \in σ})}^{4}

2

T = (\frac{P}{A \in σ})

3

T = {(\frac{A \in σ}{P})}^{\frac{1}{4}}

4

T = {(\frac{P}{A \in σ})}^{\frac{1}{4}}

Explanation:

D Radiant power $P$ is defined as energy radiated per unit area $i e$
$P = A \in σ T^{4}$
$T = {(\frac{P}{A \in σ})}^{1 / 4}$

MP PMT-2009

Heat Transfer

149607 Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. First and third plates are maintained at absolute temperatures $2 T$ and $3 T$ respectively.
Temperature of the middle plate in steady state is $s$

1

{(\frac{65}{2})}^{\frac{1}{4}} T

2

{(\frac{97}{4})}^{\frac{1}{4}} T

3

{(\frac{97}{2})}^{\frac{1}{4}} T

4

(97)^{\frac{1}{4}} T

Explanation:

C Let $T^{'}$ be the temperature of middle plate. In steady state, energy absorbed by middle plate is equal to energy released by middle plate.
$σ A [(3 T)^{4} - {(T^{'})}^{4}] = σ A [{(T^{'})}^{4} - (2 T)^{4}]$
$2 {(T^{'})}^{4} = 97 T^{4}$
$T^{'} = {(\frac{97}{2})}^{1 / 4} T$

AP EAMCET (22.04.2018) Shift-1

Heat Transfer

149591 Evening Sun is not as hot as the mid day sun. What is the reason?

1 In the evening radiations travel slowly

2 In the evening the temperature of the sun decreases

3 Ozone in atmosphere absorbs more light in the evening

4 In the evening radiations travel a long distance through atmosphere

NDA (I) 2008

Heat Transfer

149443 For any material, if $R, T$ and $A$ represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true

1

R = 1, T = 0, A = 0

2

R = 1, T = 1, A = 0

3

R = 0, T = 1, A = 1

4

R = 0, T = 0, A = 1

5

R = 0, T = 1, A = 0

Explanation:

D We know the relation between $R, T$ and $A$ is $A + T + R = 1$ (i)
for ideal black body, reflection co-efficient and transparent co-efficient is zero then from equation (i) $R = 0, T = 0, A = 1$

Kerala CEE -2018

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