Physics

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(a), (d) During the process AB temperature of the system is 0⁰C . hence it represents phase change that is transformation of ice into water while temperature remains 0⁰C.

BC represents rise in temperature of water from 0⁰C to 100⁰C. now water starts converting into steam which is represented by CD.

Which is only represents by a, d options

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer. (b)

Explanation-The charges may be located anywhere inside the surface, if the surface      is so chosen that there are some charges inside and some outside, the electric field on the left side of equation is due to all charges, both inside and outside S.

This is a multiple choice answer as classified in NCERT Exemplar

(b), (c) Smaller gulab jamun having least surface area hence they will be heated first. As in case of smaller gulab jamun heat radiates will be less.

Similarly smaller pizzas are heated before bigger ones because of smaller surface area.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer. (d) 

Explanation- Total flux inside a conducting sphere is depend upon the algeabric sum of total charge inside that surface, which is same for all fig. As it does not depend upon shape of a body

This is a multiple choice answer as classified in NCERT Exemplar

(b), (d) T_x=T_y when x and y are in thermal equilibrium.

T_{x $\ne$} T_Z when x and z are not in thermal equilibrium.

T_{y $\ne$} T_Z

Hence y and z are not In thermal equilibrium.

Given T_{x $\ne$} T_y

And T_{x $\ne$} T_Z

We cannot say about equilibrium of y and z.

They may or may not in thermal equilibrium

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a)

Explanation- when a positive point charge is brought near an isolated conducting sphere without touching the sphere, then the free electron in the sphere are attracted towards the positive charge. This leaves an excess positive charge on right side of sphere . And also by induction the negative charge is setup across left side. So field lines first goes from positive charge (+q) to negative charge of sphere then from positive charge of sphere to negative charge anywhere in the universe.

This is a multiple choice answer as classified in NCERT Exemplar

(c) density = mass/volume as density is same so volume is also same.

According to Stefan's law H $\propto$ AT⁴  where A is the area and T is the temperature

H_sphere:H_cube:H_plate= A_sphere:A_cube:A_plate

As A_plate is maximum.

Hence the plate will cool the fastest.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer.   (a)

Explanation-The force between (q1, q2) and (q1, q3) is must be attractive to net forces act in positive direction of x . so q1 must be negative. But if we place a positive charge Q in positive direction of x then it must be attractive towards along x-axis. So it will be attractive towards positive x axis. 

This is a multiple choice answer as classified in NCERT Exemplar

(d) Let radius of sphere be R . as the temperature increases radius of the sphere increases.

Original volume V_o= $\frac{4}{3}\pi R$ ³

Coefficient linear expansion = $\alpha$

Coefficient of volume expansion =3 $\alpha$

$\frac{dV}{VdT}=$ 3 $\alpha$  , dV= 4 $\pi$ R³  $\alpha ?T$ =increase in volume