Tag: physics

Questions Related to physics

Name the device for detecting and measuring small amount of thermal energy.

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. Pyranometer

  2. Pyrometer

  3. Barrater

  4. Bolometer

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Correct Option: D

State whether true or false :
A gas thermometer measures temperature with the variation in pressure or volume of a gas.

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. True

  2. False

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Correct Option: A
Explanation:

A gas thermometer measures temperature by the variation in volume or pressure of a gas.This thermometer functions by Charles's Law. Charles's Law states that when the temperature of a gas increases, so does the volume.

Using Charles's Law, the temperature can be measured by knowing the volume of gas at a certain temperature by using the formula, written below. Translating it to the correct levels of the device that is holding the gas. This works on the same principle as mercury thermometers.

${\displaystyle V\propto T\,},$
or

${\displaystyle {\dfrac {V}{T}}=k} $
T is the temperature.

V is the volume.

The resistance of a platinum wire of a platinum resistance thermometer at the ice point is $5 \Omega$ and at steam point is $5.4 \Omega$. When the thermometer is inserted in a hot bath, the resistance of the platinum wire is $6.2 \Omega$. Find the temperature of the hot bath.

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. $300^\circ C$

  2. $30^\circ C$

  3. $3000^\circ C$

  4. $300 \ K$

Show answer
Correct Option: A
Explanation:
Given,

Resistance of platinum wire at ice point, $R _0=5\,\Omega$

Resistance of platinum wire at hot bath $R _H=6.2\,\Omega$

Temperature at hot bath $T _H=?$

We have,

$R _T=R _0[1+\alpha(T-T _0)]$

$\implies R _{100}=R _0[1+\alpha(T _{100}-T _0)]$

$\implies 5.4=5[1+\alpha(100-0)]$

$\implies \dfrac{5.4}{5}-1=100\alpha$

$\implies \alpha=\dfrac{1}{1250}  \, ^0 C^{-1}$

Also,

$R _H=R _0[1+\alpha (T _H-T _0)]$

That is,

$6.2=5[1+\dfrac{1}{1250}(T _H-0)]$

$\dfrac{6.2}{5}-1=\dfrac{1}{1250}\times T _H$

$\implies T _H=300^0 C$


A thermometer uses 

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. water

  2. mercury

  3. air

  4. none

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Correct Option: B

45 gm of alcohol are needed to completely fill up a weight thermometer at $15^{\circ}C$. Find the weight of alcohol which will overflow when the weight thermometer is heated to $33^{circ}C$.
(Given ${ \gamma  } _{ a }=121\times { 10 }^{ -5 }{ { \circ  } _{ C } }^{ -1 }$

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. 0.96 gm

  2. 0.9 gm

  3. 1 gm

  4. 2 gm

Show answer
Correct Option: C

Consider two thermometers $T _1$ and $T _2$ of equal length which can be used to measure temperature over the range $\theta _1$ and $\theta _2$. $T _1$ contains mercury as thermometric liquid while $T _2$ contains bromine. The volumes of the two liquids are the same at the temperature $\theta _1$. The volumetric coefficients of expansion of mercury and bromine are $18\times 10^{-5}K^{-1}$ and $108\times 10^{-5}K^{-1}$, respectively. The increase in length of each liquid is the same for the same increase in temperature. If the diameters of the capillary tubes if the two thermometers are $d _1$ and $d _2$ respectively, then the ratio $d _1:d _2$ would be closest to.

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. $6.0$

  2. $2.5$

  3. $0.5$

  4. $0.4$

Show answer
Correct Option: D
Explanation:

Increase in length of each liquid is same 

$\dfrac{\Delta V _{hg}}{\pi d _1^2}=\dfrac{\Delta V _{br}}{\pi d _2^2}$
$\dfrac{\Delta V _{hg}\Delta\theta}{\pi d _1^2}=\dfrac{\Delta V _{br}\Delta\theta}{\pi d _2^2}$
$\dfrac{d _12}{d _2^2}=\dfrac{\gamma _{hg}}{\gamma _{br}}=\dfrac{1}{6}$
$\dfrac{d _1}{d _2}=0.4$

$\begin{array} { l } { \text { Energy required to dissociate } 4 \mathrm { g } \text { of gaseous } } \ { \text { hydrogen into free gaseous atoms is } 208 \mathrm { Kcal {at}  }  } \ {  25 ^ { \circ } \mathrm { C } \text { . The bond energy of } \mathrm { H } - \mathrm { H } \text { bond will be : } } \end{array}$ .

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. $1.04Kcal$

  2. $10.4Kcal$

  3. $104Kcal$

  4. $1040Kcal$

Show answer
Correct Option: C
Explanation:
Given heat of atmosphere $40=260\ Kcal$
$2H _{2} \rightarrow 4H$
$\triangle H = 208\ Kcal$
$20 \rightarrow 1\ mole$
$40 \rightarrow 2 \ mole$
$Hene \ 2 H-H$ bonds area brown $bg $
$20\ kcal $ energy so in order to break $1\ H-H$ bound we required $\dfrac{208}{2}= 104\ Kcal$
Hence the bond energy of $H-H$ bound will be $=104\ kcal$

Which of the following statements is correct?

physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

  1. Air escaping from a punctured tyre feels cold

  2. When a gas under high pressure is permitted to expand into a region of low pressure, it gains in temperature

  3. The reading on a thermometer immersed in boiling water varies as the heat increases or decreases above the boiling point

  4. None of the above statements is correct

Show answer
Correct Option: A
Explanation:

Option (A) is correct. 

Reason - The air is contained at high pressure in the tube. When it escapes through a small hole, it suddenly expands. A large amount of heat is absorbed in the process of expansion resulting in considerable fall in its temperature. This is why the escaping air feels cold.

Why is the Sun important for us?

physics movement of the earth properties of stars life cycle of stars solar system and its planets types of galaxies galaxies

  1. It is the main source of light and heat.

  2. It is the source of energy.

  3. Its gravitational force keeps all planets and other heavenly bodies in place.

  4. All of the above.

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Correct Option: D
Explanation:

Sun is very important to us as it is the main source of light and heat, i.e, the main source of energy. Besides, its gravitational force keeps all planets and other heavenly bodies in place.

The highest number of atoms in the Sun are of:

physics movement of the earth properties of stars life cycle of stars solar system and its planets types of galaxies galaxies

  1. hydrogen

  2. helium

  3. oxygen

  4. nitrogen

Show answer
Correct Option: A
Explanation:

Percentage of total number of atoms:
Hydrogen: $91.2$
Helium: $8.7$
Oxygen: $0.078$
Nitrogen: $0.0088$