Q: If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be

let us assume initial Temperature \$T_1=T\$ then final will be \$T_2=\dfrac{50}{100}T+T=\dfrac{150}{100}T=\dfrac{15}{10}T\$ energy radiated \$e_1=\sigma A T_1^4\quad \left(1\right)\$ \$e_2=\sigma A T_2^4\quad \left(2\right)\$ \$\%\$ increase in radiation \$=\dfrac{e_2-e_1}{e_1}\times 100\$ \$=\dfrac{\sigma A T_2^4-\sigma A T_1^4}{\sigma A T_1^4}\times 100\$ \$\dfrac{\left(\dfrac{15}{10}T\right)^4-T^4}{T^4}\times 100\$ \$\dfrac{15^4-10^4}{10^4}\times 10^2\$ \$\dfrac{50625-10000}{10^2}\$ \$=406.25\$ \$\approx 400\%\$ Hence \$(d)\$ option is correct.

Question 1

Give reasons.(a) After a hot sunny day, we sprinkle water on the roof or open ground.(b) Perspiration keeps our body cold.(c) Ice is rubbed on burnt part of the skin

Accepted Answer

Part (a) on hot sunny day, we sprinkle water on roof or open ground because the water can absorb the heat and get converted into vapours.Since water absorb heat so temperature of surrounding fell down and we get cooling.Part (b) As perspiration takes place it will gives sweat, sweat will absorb the heat from our body it makes your skin feel cooler when its wet.Hence in evaporation of sweat will cause absorption of heat making your body cold.Part (c) Ice has latent heat, it will absorb the heat from burnt skin. Ice get converted into liquid. So it will absorb heat and gives relaxation from burning.

Question 2

The movement of water being heated in a pot on a stove is an example of

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Question 3

A student took an iron rod and a wooden rod and wrapped each of them in a piece of paper. These were then heated as shown. It was found that the paper around the iron rod does not burn whereas the one around the wooden rod catches fire.It is because

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Question 4

If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be

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let us&#10;assume initial Temperature $T_1=T$ then final will be&#10;&#10;$T_2=\dfrac{50}{100}T+T=\dfrac{150}{100}T=\dfrac{15}{10}T$&#10;&#10;energy&#10;radiated &#10;&#10;$e_1=\sigma&#10;A T_1^4\quad \left(1\right)$&#10;&#10;$e_2=\sigma&#10;A T_2^4\quad \left(2\right)$&#10;&#10;$\%$&#10;increase in radiation &#10;&#10;$=\dfrac{e_2-e_1}{e_1}\times&#10;100$&#10;&#10;$=\dfrac{\sigma&#10;A T_2^4-\sigma A T_1^4}{\sigma A T_1^4}\times 100$&#10;&#10;$\dfrac{\left(\dfrac{15}{10}T\right)^4-T^4}{T^4}\times&#10;100$&#10;&#10;$\dfrac{15^4-10^4}{10^4}\times&#10;10^2$&#10;&#10;$\dfrac{50625-10000}{10^2}$&#10;&#10;$=406.25$&#10;&#10;$\approx&#10;400\%$&#10;&#10;Hence $(d)$ option is correct.

Question 5

Two thermometers are used to record the temperature of a room and the bulb of one is wrapped in a wet hanky.

Accepted Answer

The temperature recorded by the dry bulb thermometer will be greater. Due to evaporation cooling is caused which lowers the temperature of the bulb wrapped in a wet hanky.

Question 6

Boojho has three thermometers as shown in above Figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose?

Accepted Answer

The image (I) and (III) are the clinical thermometers that are used to measure the body temperature only.The correct answer is option (a). Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.

Question 7

A metal spoon is placed in one of two identical cups of hot coffee. Why does the cup with the spoon have a lower temperature after a few minutes ?

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Question 8

Mercury is often used in clinical thermometers. Which one of the following properties of mercury is not a reason for this ?

Accepted Answer

Mercury is used in thermometer as it has a high coefficient of expansion so even the smallest change in temperature can be observed, it is shiny so that we can see the level of mercury clearly and it is liquid for a wide range of temperature. But, high density of mercury is not the reason for its use in clinical thermometers.Hence, OPTION : D.

Question 9

Two thermometers are constructed in such a way that one has a spherical bulb and the other has elongated cylindrical bulb. The bulbs are made of same material and thickness. Then :

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Question 10

Though air is a bad conductor yet a body kept in air loses heat quickly.

Accepted Answer

The heat loss is mainly due to radiation.

Heat

Physics
8932 Views

Give reasons.
(a) After a hot sunny day, we sprinkle water on the roof or open ground.
(b) Perspiration keeps our body cold.
(c) Ice is rubbed on burnt part of the skin

The movement of water being heated in a pot on a stove is an example of

A student took an iron rod and a wooden rod and wrapped each of them in a piece of paper. These were then heated as shown. It was found that the paper around the iron rod does not burn whereas the one around the wooden rod catches fire.It is because

If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be

Two thermometers are used to record the temperature of a room and the bulb of one is wrapped in a wet hanky.

Boojho has three thermometers as shown in above Figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose?

A metal spoon is placed in one of two identical cups of hot coffee. Why does the cup with the spoon have a lower temperature after a few minutes ?

Mercury is often used in clinical thermometers. Which one of the following properties of mercury is not a reason for this ?

Two thermometers are constructed in such a way that one has a spherical bulb and the other has elongated cylindrical bulb. The bulbs are made of same material and thickness. Then :

Though air is a bad conductor yet a body kept in air loses heat quickly.

The heat loss is mainly due to radiation.

Heat

Physics 8932 Views

Give reasons. (a) After a hot sunny day, we sprinkle water on the roof or open ground. (b) Perspiration keeps our body cold. (c) Ice is rubbed on burnt part of the skin

The movement of water being heated in a pot on a stove is an example of

A student took an iron rod and a wooden rod and wrapped each of them in a piece of paper. These were then heated as shown. It was found that the paper around the iron rod does not burn whereas the one around the wooden rod catches fire.It is because

If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be

Two thermometers are used to record the temperature of a room and the bulb of one is wrapped in a wet hanky.

Boojho has three thermometers as shown in above Figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose?

A metal spoon is placed in one of two identical cups of hot coffee. Why does the cup with the spoon have a lower temperature after a few minutes ?

Mercury is often used in clinical thermometers. Which one of the following properties of mercury is not a reason for this ?

Two thermometers are constructed in such a way that one has a spherical bulb and the other has elongated cylindrical bulb. The bulbs are made of same material and thickness. Then :

Though air is a bad conductor yet a body kept in air loses heat quickly.

The heat loss is mainly due to radiation.

Physics
8932 Views

Give reasons.
(a) After a hot sunny day, we sprinkle water on the roof or open ground.
(b) Perspiration keeps our body cold.
(c) Ice is rubbed on burnt part of the skin