Which of the following statements is true/correct - Vidyadip

MCQ

Which of the following statements is true/correct

A
During clear nights, the temperature rises steadily upward near the ground level
✓
Newton's law of cooling, an approximate form of Stefan's law, is valid only for natural convection
C
The total energy emitted by a black body per unit time per unit area is proportional to the square of its temperature in the Kelvin scale
D
Two spheres of the same material have radii $1m$ and ${S_1}$ and temperatures $4000 K$ and $2000 K$ respectively. The energy radiated per second by the first sphere is greater than that radiated per second by the second sphere

✓

Answer

Correct option: B.

Newton's law of cooling, an approximate form of Stefan's law, is valid only for natural convection

b
(b) During clear nights object on surface of earth radiate out heat and temperature falls. Hence option $(a)$ is wrong.

The total energy radiated by a body per unit time per unit area $E \propto T^4$. Hence option $(c)$ is wrong.

Energy radiated per second is given by $\frac{Q}{t} = PA\varepsilon \sigma {T^4}$

==> $\frac{{{P_1}}}{{{P_2}}} = \frac{{{A_1}}}{{{A_2}}}.{\left( {\frac{{{T_1}}}{{{T_2}}}} \right)^4} = {\left( {\frac{{{r_1}}}{{{r_2}}}} \right)^2}.{\left( {\frac{{{T_1}}}{{{T_2}}}} \right)^4} = {\left( {\frac{1}{4}} \right)^2}\left( {\frac{{4000}}{{200}}} \right) = \frac{1}{1}$
$\because P1 = P2$ , hence option $(d)$ is wrong.

Newton's law is an approximate form of Stefan's law of radiation and works well for natural convection. Hence option $(b)$ is correct.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from 10.2 , transmission of heat→10.2 , transmission of heat — all question types→Physics STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body

The period of a simple pendulum measured inside a stationary lift is found to be $T$. If the lift starts accelerating upwards with acceleration of $g/3,$ then the time period of the pendulum is

Plane angle and solid angle have :

A body of mass $5\ kg$ undergoes a change in speed from $20$ to $0.20\ m/ s.$ The momentum of the body would:

Rain is falling vertically with a speed of $30\,ms^{-1}$ . A woman rides a bicycle with a speed of $12\,ms^{-1}$ in east to west direction. She should hold her umbrella

A particle of mass $M=0.2 kg$ is initially at rest in the $x y$-plane at a point $( x =-l, y =-h)$, where $l=10 m$ and $h=1 m$. The particle is accelerated at time $t =0$ with a constant acceleration $a =10 m / s ^2$ along the positive $x$-direction. Its angular momentum and torque with respect to the origin, in SI units, are represented by $\vec{L}$ and $\vec{\tau}$, respectively. $\hat{i}, \hat{j}$ and $\hat{k}$ are unit vectors along the positive $x , y$ and $z$-directions, respectively. If $\hat{k}=\hat{i} \times \hat{j}$ then which of the following statement($s$) is(are) correct?

$(A)$ The particle arrives at the point $(x=l, y=-h)$ at time $t =2 s$.

$(B)$ $\vec{\tau}=2 \hat{ k }$ when the particle passes through the point $(x=l, y=-h)$

$(C)$ $\overrightarrow{ L }=4 \hat{ k }$ when the particle passes through the point $(x=l, y=-h)$

$(D)$ $\vec{\tau}=\hat{ k }$ when the particle passes through the point $(x=0, y=-h)$

An object while moving may not have:

A refrigerator is to maintain eatables kept inside at $9^{\circ} C .$ If room temperature is $36^{\circ} C$ calculate the coefficient of performance.

A body weighs $700\, gm$ weight on the surface of the earth. How much will it weigh on the surface of a planet whose mass is $\frac{1}{7}$ and radius is half that of the earth ...... $gm\, wt$

If the mean free path of atoms is doubled then the pressure of gas will become