Tag: energy transformations and energy transfers

Questions Related to energy transformations and energy transfers

The temperature inside and outside a refrigerator are $273\ K$ and $300\ K$ respectively Assuming that the refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be nearly

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $11\ J$

  2. $22\ J$

  3. $33\ J$

  4. $50\ J$

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Correct Option: D

The height of the Niagara falls is $50$ metres, $(1 cal= 4.2 \mathrm\ { J }).$  Assume its mechanical energy can be completely converted into heat energy.

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. Heat energy gained by each gram of water is $49 \times 10 ^ { 5 }\ \mathrm { cal }$

  2. Rise in temperature of water is $0.166^{ o }\ C/g$

  3. Rise in temperature of water is $0.12^{ o }\ C$

  4. Heal energy gained is $500\ joule/g$

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Correct Option: C,D

The units of fore and length are made three times of their earlier values. Earlier the energy of a system was $81\ J$. What will be the energy of the same system in new units?

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $243$

  2. $729$

  3. $9$

  4. $None\ of\ the\ above$

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Correct Option: B

When $1\ gm$. of water at $100^{\circ}C$ is converted into steam occupies $1671\ c.c.$ The amount of work done in converting water into steam is

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $167\ J$

  2. $180\ J$

  3. $184\ J$

  4. $2098\ J$

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Correct Option: D

$1$ calorie is the heat required to increase the temperature of $1g$ of water by $1 ^ { \circ } \mathrm { C }$ from:

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $13.5 ^ { \circ } \mathrm { C } \text { to } 14.5 ^ { \circ } \mathrm { C } \text { at } 76 \mathrm { mm } \text { of } \mathrm { Hg }$

  2. $14.5 ^ { \circ } \mathrm { C } \text { to } 15.5 ^ { \circ } \mathrm { C } \text { at } 760 \mathrm { mm } \text { of } \mathrm { Hg }$

  3. $13.5 ^ { \circ } \mathrm { C } \text { to } 15.5 ^ { \circ } \mathrm { Cat } 76 \mathrm { mm } \text { of } \mathrm { Hg }$

  4. $15.5 ^ { \circ } \mathrm { C } \text { to } 16.5 ^ { \circ } \mathrm { C } \text { at } 700 \mathrm { mm } \text { of } \mathrm { Hg }$

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Correct Option: A

If the amount of heat given to a system is $35\, J$ and the amount of work done on the system is $15\, J$, then the change in internal energy of the system is

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $- 50\, J$

  2. $20\, J$

  3. $30\, J$

  4. $50\, J$

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Correct Option: D
Explanation:

Given,

$\Delta Q=+35J$
$\Delta W=-15J$
$\Delta U=?$
From law of thermodynamic,
$\Delta Q=\Delta U+\Delta W$
$\Delta U=\Delta Q-\Delta W$
$\Delta U=35-(-15)$
$\Delta U=35+15$
$\Delta U=50J$
The correct option is D. 

A geyser heats water flowing at the rate of 3.0 liters per minute from ${ 27 }^{ \circ  }C$ to ${ 77 }^{ \circ  }C$. If the geyser operates on a gas burner, the rate of consumption of the fuel if its heat of combustion is $4.0\times { 10 }^{ 4 }J/g$ per minute is

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $15.75g$

  2. $4 g$

  3. $0.3 g$

  4. $0.16 g$

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Correct Option: A

A certain quantity of heat energy is given to a diatomic ideal gas which expands at constant pressure. The fraction of the heat energy that is converted into work is 

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $\dfrac 2 5$

  2. $\dfrac 2 7$

  3. $\dfrac 1 5$

  4. $\dfrac 5 7$

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Correct Option: D
Explanation:

Supplied heat at constant pressure, 

$\Delta Q=nC _P \Delta T$
Change in internal energy,
$\Delta U=nC _V \Delta T$
ratio, $\dfrac{\Delta U}{\Delta Q}=\dfrac{nC _V \Delta T}{nC _P \Delta T}=\dfrac{C _V}{C _P}$. . . . . . . . .(1)
For diatomic ideal gas,
$C _P=\dfrac{7R}{2}\,  ,  C _V=\dfrac{5R}{2}$
From equation (1), we get
$\dfrac{\Delta U}{\Delta Q}=\dfrac{5R/2}{7R/2}=\dfrac{5}{7}$
$(5/7)^{th}$ part of heat supplied is used to increase internal energy.

A hammer of mass 1$\mathrm { kg }$ having speed of 50$\mathrm { m } / \mathrm { s }$ , hit a iron nail of mass 200$\mathrm { gm }$ . If specific heat of iron is 0.105 cal/gm'C and half the energy is converted into heat, the raise in temperature of nail is

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $7.1 ^ { \circ } C$

  2. $9.2 ^ { \circ } \mathrm { C }$

  3. $10.5 ^ { \circ } C$

  4. $12.1 ^ { \circ } \mathrm { C }$

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Correct Option: A

In case of explosion of a bomb which of the following does not change?

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. Chemical energy

  2. Total energy

  3. Kinetic energy

  4. Mechanical energy

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Correct Option: B
Explanation:

The chemical energy possessed by the bomb after explosion converts into heat energy, sound energy, light energy i.e. into different forms of energy but remains conserved. Hence, total energy of bomb does not change, but kinetic and mechanical energy changes.