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Solution for Class 12, Physics

Question 1

8. Consider the situation shown in figure (31-E31). The plates of the capacitor have plate area

A

and are clamped in the laboratory. The dielectric slab is released from rest with a length

a

inside the capacitor. Neglecting any effect of friction or gravity, show that the slab will execute periodic motion and find its time period.

Topic:

Electrostats

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Question 2

42. A block is kept on the floor of an elevator at rest. The elevator starts descending with an acceleration of

12 m / s^{2}

. Find the displacement of the block during the first

0.2 s

after the start. Take

g = 10 m / s^{2}

Topic:

Mechanics

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Question 3

103. A thin convex lens

L

(refractive index

= 1.5

) is placed on a plane mirror

M

. When a pin is placed at

A

, such that

O A = 18 cm

, its real inverted image is formed at

A

itself, as shown in figure. When a liquid of refractive index

m u_{l}

is put between the lens and the mirror, the pin has to be moved to

A^{p r im e}

, such that

O A^{p r im e} = 27 cm

, to get its inverted real image at

A^{p r im e}

itself. The value of

m u

, will be

{"(2019 Main)","(b) $2$ ","(c) $\frac{4}{3}$ ","(d) $\frac{3}{2}$ "}

Topic:

Optics

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Question 4

A metallic solid is placed in a uniform electric field. The lines of force follow the path(s) shown in the figure as:

Topic:

Electrostats

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Question 5

A string of length

L

is fixed at one end and carries a mass

M

at the other end. The string makes

\frac{2}{π}

revolutions per second around the vertical axis through the fixed end as shown in the figure, then tension in the string is :-

$ML$
$2 ML$
$4 ML$
$16 ML$

Topic:

Mechanics

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Question 6

A cube and a sphere of same material, same total surface area, at same temperature are placed in same evacuated space one by one. The ratio of their initial rate of cooling is

$1 : \frac{π}{2}$
$1 : \frac{π}{6}$
$1 : \frac{π}{2}$
$1 : \frac{π}{6}$

Topic:

Heat & Thermodynamics

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Question 7

A cube and a sphere of same material, same total surface area, at same temperature are placed in same evacuated space one by one. The ratio of their initial rate of cooling is

1: $\frac{π}{2}$
$1 : \frac{π}{6}$
$1 : \frac{π}{2}$
$1 : \frac{π}{6}$

Topic:

Heat & Thermodynamics

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Question 8

A capacitor is made of two square plates each of side

^{p r im e}

making a very small angle

α

between them, as shown in figure. The capacitance will be close to:

l e f t (1 + \frac{α a}{d} i g h t)

$\frac{ϵ _{0} a ^{2}}{d} l e f t (1 - \frac{3 α a}{2 d} i g h t)$

Topic:

Electrostats

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Question 9

A capacitor is made of two square plates each of side

^{p r im e}

making a very small angle

α

between them, as shown in figure. The capacitance will be close to:

l e f t (1 + \frac{α a}{d} i g h t)

$\frac{ϵ _{0} a ^{2}}{d} l e f t (1 - \frac{3 α a}{2 d} i g h t)$

Topic:

Electrostats

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Question 10

A capacitor is made of two square plates each of side

^{p r im e}

making a very small angle

α

between them, as shown in figure. The capacitance will be close to:

l e f t (1 + \frac{α a}{d} i g h t)

$\frac{ϵ _{0} a ^{2}}{d} l e f t (1 - \frac{3 α a}{2 d} i g h t)$

Topic:

Mechanics

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Question 11

A battery of

3.0 V

is connected to a resistor dissipating

0.5 W

of power. If the terminal voltage of the battery is

2.5 V

, the power dissipated within the internal resistance is :

Topic:

Electrostats

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Question 12

q

resistance

100Ω2

, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is (2017 Main)

$225 Wb$
$250 Wb$
$275 Wb$
$200 Wb$

Topic:

Magnetism, EMI & AC

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Question 13

When a negatively charged rod is brought near the cap of a gold leaf electroscope whose case is earthed, then

Leaves will have induced positive charge
Positive charge is induced on one leaf and negative on the other
No charge is induced on the leaves
The leaf has an induced negative charge

Topic:

Electrostats

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Question 14

2. What is the electric flux through a cube of side

1 cm

which encloses an electric dipole? All india 2015

Topic:

Electrostats

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Question 15

A cubical Gaussian surface encloses a spherical conductor at its centre. If the conductor carries a charge of 24 C, the TNEI over any one face of the cube is

greater than $4 C$
equal to $4 C$
less than 4 C
greater than, equal to or less than $4 C$ .

Topic:

Electrostats

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Question 16

A cubical Gaussian surface encloses a spherical conductor at its centre. If the conductor carries a charge of 24 C, the TNEI over any one face of the cube is

greater than $4 C$
equal to $4 C$
less than $4 d o t C$
greater than, equal to or less than $4 C$ .

Topic:

Electrostats

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Question 17

ii) In Si units, the differential equation of an SHM is d

x

d i^{2} = - 36 x

. Find its angular frequency.

Topic:

Waves & Oscillation

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Question 18

12 The number of silicon atoms per

m^{3}

5 \times 1 0^{28}

. This is doped simultaneously with

5 \times 1 0^{22}

atoms per

m^{3}

of Arsenic and

5 \times 1 0^{20}

per

m^{3}

atoms of Indium. Calculate the number of electrons and holes. Given that

n_{l} = 1.5 \times 1 0^{16} m^{- 3}

. Is the material

n

-type or

p

-type?

Topic:

Atoms, Nuclei & Dual nature

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Question 19

As shown in figure there is a spring block system. Block of mass

500 g

is pressed against a horizontal spring fixed at one end to compress the spring through

5.0 cm

. The spring constant is

500 N / m

. When released, the block moves horizontally till it leaves the spring. Calculate the distance where it will hit the ground

4 m

below the spring?

Topic:

Mechanics

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Question 20

65 The potential energy between two atoms in a molecule is given by,

U_{(x)} = \frac{a}{x ^{12}} - \frac{b}{x ^{6}}

, where a and

b

are positive constants and

x

is the distance between the atoms. The system is in stable equilibrium when -

Topic:

Mechanics

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Solution for Class 12, Physics

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