Physics

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- No field inside a hollow body because if we give charge to a hollow body whole charge is distributed outside its surface. This phenomenon is called electrostatic shielding which is used to protect things from electric field or electric shock.

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- if the total charge inside a surface is zero it does not mean that electric field is zero may it will flow from inside to outside or vice versa. But if electric field is zero then charge must be zero .

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- In any neutral atom, the number of electrons and protons are equal, and the protons and electrons are bound into an atom with distinct and independent existence. Electrostatic fields are caused by the presence of excess charges. But there can be no excess charge of an isolated conductor. So, the electrostatic fields inside a conductor is zero

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation – (i) surface density=charge/area= -Q/4 $\pi R$ ₁²

                        (ii) surface density=charge/area= +Q/4 $\pi R$ ₂²

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(d) As  ${\alpha }_{Al}>{\alpha }_{steel}$ , aluminium will expand more . so it would have larger radius of curvature. So aluminium will expand and will outside region.

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Explanation- Electric flux through a dipole is always zero, because the positive and negative charges cancel each other out

This is a short answer type question as classified in NCERT Exemplar

The first option kept water warmer because according to newton's law of cooling the rate of loss of heat is directly proportional to the difference of temperature of the body and the surroundings and in the first case temperature difference is less. So rate of loss of heat will be less.

This is a short answer type question as classified in NCERT Exemplar

Mass of water m =100

Change in temperature $?T=0—10=10°C$

Specific heat of water S_w= 1cal/g $°$ C

Latent heat of fusion of water L_fusion= 80cal/g

Heat required to bring water in super cooling from -10 to 0 $°C$

Q= ms $?t=100**10=1000cal$

Let m gram of ice be melted Q= mL

m=Q/L=1000/80= 12.5g

This is a short answer type question as classified in NCERT Exemplar

Increasing pressure at 0⁰C and 1 atm takes ice into liquid state and decreasing pressure in liquid state at 0⁰C and 1 atm takes to ice state.

When crushed ice is squeezed, some of it melts, filling up the gap between ice flakes upon releasing pressure. This water freezes, binding all ice flakes and making the ball more stable.

This is a short answer type question as classified in NCERT Exemplar

Let the mass and length of a uniform rod be M and l respectively.

Moment of inertia of the rod about its perpendicular bisector I= ml²/12

Increase in length of the rod when temperature is increased by $?$ T is given by

$?l=l\alpha ?T$

So new moment of inertia of the rod = $\frac{M}{12}({l+?l)}^2$ = $\frac{M}{12}\left(l^2+?l^2+2l?l\right)$

As change in length $?l$  is very small therefore neglecting $?l^2$  so we  get

I'= $\frac{M}{12}\left(l^2+2l?l\right)$ = l+mI $\frac{?l}{6}$

Increase in moment of inertia = $\frac{Ml?l}{6}=2*{\left(\frac{m{l}^2}{12}\right)}^1\frac{?l}{l}=2I\alpha ?T$