###### Advertisements

###### Advertisements

A metal ball cools from 64 ^{°}C to 50 ^{°}C in 10 minutes and to 42 ^{°}C in next 10 minutes. The ratio of rates of fall of temperature during the two intervals is _______.

#### Options

`4/7`

`7/4`

2

2.5

###### Advertisements

#### Solution

`7/4`

Rate of fall of temperature in first 10 minutes = R_{1} = `(64 - 50)/10`.°C/min = 1.4°C/min

Rate of fall of temperature in next 10 minutes = R_{2} = `(50 - 42)/10`.°C/min = 0.8°C/min

⇒ `R_1/R_2 = 7/4`

#### APPEARS IN

#### RELATED QUESTIONS

Define emissive power and coefficient of emmision of a body.

A metal sphere cools at the rate of 4°C / min. when its temperature is 50°C. Find its rate of cooling at 45°C if the temperature of surroundings is 25°C.

Two copper spheres of radii 6 cm and 12 cm respectively are suspended in an evacuated enclosure. Each of them are at a temperature 15°C above the surroundings. The ratio of their rate of loss of heat is.................

- 2:1
- 1:4
- 1:8
- 8:1

The dimensions of emissive power are

A pinhole is made in a hollow sphere of radius 5 cm whose inner wall is at temperature 727^{o}C. Find the power radiated per unit area. [Stefan’s constant σ = 5.7 x 10^{-8} J/m^{2} s K4 , emissivity (e) = 0.2]

Compute the temperature at which the r.m.s. speed of nitrogen molecules is 832 m/s. [Universal gas constant, R = 8320 J/k mole K, molecular weight of nitrogen = 28.]

The light from the Sun is found to have a maximum intensity near the wavelength of 470 nm. Assuming the surface of the Sun as a black body, the temperature of the Sun is _____________.

[Wien's constant b = 2 .898 x l0^{- 3}mK]

The susceptibility of magnesium at 300 K is 2.4 x 10^{-5}. At what temperature will the susceptibility increase to 3.6 x 10^{-5}?

1000 tiny mercury droplets coalesce to form a bigger drop. In this process, temperature of the drop _______ .

(A) increases

(B) may increase or decrease

(C) decreases

(D) does not change

A body cools from 62°C to 54°C in 10 minutes and to 48°C in the next 10 minutes. Find the temperature of the surroundings.

The susceptibility of magnesium at 300K is 1.2 x 10^{-5}. At what temperature will the susceptibility increase to 1.8 X 10^{-5}?

The substance which allows heat radiations to pass through is _______.

(A) iron

(B) water vapour

(C) wood

(D) dry air

The kinetic energy per molecule of a gs at temperature T is ________.

(a) `(3/2)RT`

(b) `(3/2)K_BT`

(c) `(2/3) RT`

(d) `(3/2)("RT"/M)`

A body cools from 80° C to 70° C in 5 minutes and to 62° C in the next 5 minutes. Calculate the temperature of the surroundings.

Does the temperature of a body depend on the frame from which it is observed?

Can the bulb of a thermometer be made of an adiabatic wall?

The length of a brass rod is found to be less on a hot summer day than on a cold winter day as measured by the same aluminium scale. Can we conclude that brass shrinks on heating?

The density of water at 4°C is supposed to be 1000 kg m^{–3}. Is it same at sea level and at high altitude?

Which of the curves in the following figure represents the relation between Celsius and Fahrenheit temperatures?

Which of the following pairs may give equal numerical values of the temperature of a body?

If the temperature of a uniform rod is slightly increased by ∆t, its moment of inertia I about a line parallel to itself will increase by

As the temperature is increased, the time period of a pendulum

A person's skin is more severely burnt when put in contact with 1 g of steam at 100°C than when put in contact with 1 g of water at 100°C. Explain

The atmospheric temperature in the cities on sea-coast change very little. Explain

Should a thermometer bulb have large heat capacity or small heat capacity?

Water equivalent of a body is measured in ___________ .

If heat is supplied to a solid, its temperature

(a) must increase

(b) may increase

(c) may remain constant

(d) may decrease

A concrete slab has a length of 10 m on a winter night when the temperature is 0°C. Find the length of the slab on a summer day when the temperature is 35°C. The coefficient of linear expansion of concrete is 1.0 × 10^{–5} °C^{–1}.

A railway track (made of iron) is laid in winter when the average temperature is 18°C. The track consists of sections of 12.0 m placed one after the other. How much gap should be left between two such sections, so that there is no compression during summer when the maximum temperature rises to 48°C? Coefficient of linear expansion of iron = 11 × 10^{–6} °C^{–1}.

The densities of wood and benzene at 0°C are 880 kg m^{3} and 900 kg m^{–3} , respectively. The coefficients of volume expansion are 1.2 × 10^{–3 }°C^{–1} for wood and 1.5 × 10^{–3 }°C^{–1}for benzene. At what temperature will a piece of wood just sink in benzene?

A steel wire of cross-sectional area 0.5 mm^{2}^{ }is held between two fixed supports. If the wire is just taut at 20°C, determine the tension when the temperature falls to 0°C. Coefficient of linear expansion of steel is 1.2 × 10^{–5} °C^{–1} and its Young's modulus is 2.0 × 10^{–11} Nm^{–2}.

A steel ball that is initially at a pressure of 1.0 × 10^{5 }Pa is heated from 20°C to 120°C, keeping its volume constant.

Find the pressure inside the ball. Coefficient of linear expansion of steel = 12 × 10^{–6} °C^{–1}and bulk modulus of steel = 1.6 × 10^{11} Nm^{–2}.

**Answer the following question.**

Clearly, state the difference between heat and temperature?

In hot summer after a bath, the body’s __________.

‘An object contains more heat’- is it a right statement? If not why?

Define one mole.

Explain the meaning of heat and work with suitable examples.

Temperature and Heat are ______

Our normal body temperature is ______.

Two tumblers of A and B have water at 50°C temperature. If the water from A and B is poured into tumbler C. The temperature of C is ______.

Two objects are said to be in thermal contact if they can exchange heat energy.

One day in 1922, the air temperature was measured at 59°C in the shade in Libya ______.

Heat is measured in Celsius or centigrade.

Temperature in the form of energy.

The normal temperature of our body is 37°C.

**Analogy**

Evaporation:: 100°C: Freezing:: ______.

**Give reasons for the following:**

Hot metal ball of 80° C is dipped into water of 80°C. The ball will not contract.

The degree of hotness and coldness of a body is called ______.

Two identical beakers A and B contain equal volumes of two different liquids at 60°C each and is left to cool down. Liquid in A has a density of 8 × 10^{2} kg/m^{3} and specific heat of 2000 J kg^{-1} K^{-1} while the liquid in B has a density of 10^{3} kg m^{-3} and specific heat of 4000 J kg^{-1} K^{-1}. Which of the following best describes their temperature versus time graph schematically? (assume the emissivity of both the beakers to be the same.)

An earthen pitcher loses 1 gm of water per minute due to evaporation. If the water equivalent of the pitcher is 0.5 kg and the pitcher contains 9.5 kg of water, calculate the time required for the water in a pitcher to cool to 28°C from the original temperature of 30°C. Neglect radiation effects. The latent heat of vaporization in this range of temperature is 580 Cal/gm and the specific heat of water is 1 Cal/gm°C.

Heat given to a body that raises its temperature by 1°C is ______.

The temperature of a liquid drops from 365 K to 361 K in 2 min. Find the time during which the temperature of the liquid drops from 344 K to 342 K.

(Take, room temperature = 293 K)