12th Standard English Medium Physics Reduced syllabus One mark important Questions with Answer key - 2021(Public Exam )

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Questions:

Multiple Choice Question

50 x 1 = 50

A concave mirror forms an image of sun at a distance of 12 cm from it __________.

(a)

The radius of curvature of this mirror is 6 cm

(b)

To use it as a shaving mirror, it must be held at a distance of 8 - 10 cm from the face

(c)

If an object is kept at a distance of 12 cm from it, the image formed will be same size as the object

(d)

All the above

A concave mirror is used to focus the image of a flower on a nearby well 120 cm from the flower. If a lateral magnification of 16 is desired, the distance of the flower from the mirror should be _____________.

(a)

8 cm

(b)

12 cm

(c)

80 cm

(d)

120 cm

If an object is placed 10 cm in front of a concave If an object is placed 10 cm in front of a concave height one needs a ____________.

(a)

Diminished, upright, virtual

(b)

Enlarged, upright, virtual

(c)

Diminished, inverted, real

(d)

Enlarged, upright, real

All of the following statement are correct except _____________.

(a)

The magnification produced by a convex mirror is always less than one

(b)

A virtual, erect same sized image can be obtained using a plane mirror

(c)

A virtual, erect magnified image can be formed using a concave mirror

(d)

A real, inverted, same-sized image can be formed using a convex mirror

An object 2.5 cm high is placed at a distance of 10 cm from a concave mirror of radius of curvature 30 cm. The size of the image is _______________.

(a)

9.2 cm

(b)

10.5 cm

(c)

5.6 cm

(d)

7.5 cm

One side of a glass slab is silvered as shown. A ray of light is incident on the other side at an angle of incidence i = 45°. The Refractive index of glass is given as 1.5. The deviation of the ray of light from its initial path when it comes out of the slab is ______________.

(a)

90°

(b)

180°

(c)

120°

(d)

45°

Two plane mirrors are at right angles to each other. A man stands between them and combs hair with his right hand. In how many of the images will he be seen using his right-hand __________.

(a)

None

(b)

(c)

(d)

A man is 180 cm tall and his eyes are 10 cm below the top of his head. In order to see his entire height right from toe to head, he uses a plane mirror kept at a distance of 1m from him. The minimum length of the plane mirror required is _____________.

(a)

180 cm

(b)

90 cm

(c)

85 cm

(d)

170 cm

A photon of frequency v has a momentum associated with it. If c is the velocity of light the momentum is _____________.

(a)

\(\frac{v}{c}\)

(b)

hvc

(c)

\(\frac { hv }{ { c }^{ 2 } } \)

(d)

\(\frac { hv }{ c } \)

10.

The method of making nanomaterial by assembling the atoms is called _____.

(a)

Top down approach

(b)

Bottom up approach

(c)

Cross down approach

(d)

Diagonal approach

11.

Atomic number of H-like atom with ionization potential 122.4 V for n = 1 is _____.

(a)

(b)

(c)

(d)

12.

Light transmitted by Nicol prism is, _____.

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

13.

When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as plane sheet of glass. This implies that the liquid must have refractive index, ______.

(a)

less than one

(b)

less than that of glass

(c)

greater than that of glass

(d)

equal to that of glass

14.

________ radiations are used to sterilize surgical instruments.

(a)

X-ray

(b)

(c)

(d)

Gamma

15.

The frequency of electromagnetic radiation Hertz produced was _________ Hz.

(a)

10⁸

(b)

5x10⁷

(c)

3x10⁸

(d)

6x10⁵

16.

A pure red glass plate when placed in the path of the light absorbs everything except__________.

(a)

yellow

(b)

black

(c)

green

(d)

red

17.

If V_g, V_x,V_m are speeds of gamma rays, X rays and microwaves respectively in vacuum, then ______________.

(a)

V_gx m

(b)

V_g> V_k> V_m

(c)

V_g > V_x < V_m

(d)

V_g= V_x= V_m

18.

The EM waves do not transport _______________.

(a)

energy

(b)

charge

(c)

momentum

(d)

information

19.

The angular frequency of a charged particle moving in a uniform magnetic field ____________.

(a)

depends upon the mass and velocity of the particle

(b)

depends upon mass and radius of circular path

(c)

depends upon the charge and velocity of the particle

(d)

neither depends upon the velocity nor the radius of circular path

20.

The angular momentum of an electron revolving in second order (n = 2) is _________________.

(a)

6.6 x 10^-34 Js

(b)

3.3 x 10^-34 Js

(c)

2.1 x 10^-34 Js

(d)

9.27 x 10^-34 Js

21.

The period of revolution of a charged particle inside a cyclotron does not depend on __________________.

(a)

the magnetic induction

(b)

the charge of the particle

(c)

the velocity of the particle

(d)

the mass of the particle

22.

In a thermocouple, the temperature of cold junction is 30°C and the neutral temperature is 310°C. The temperature of inversion is ______________________.

(a)

580°C

(b)

590°C

(c)

600°C

(d)

690°C

23.

When the hot and cold junctions of a thermo couple are interchanged then the thermo emf ________________.

(a)

increases

(b)

remain unchanged

(c)

decreases

(d)

increases or decreases according to nature of metals used

24.

For a given thermocouple for a given cold junction temperature, the inversion is 220°C. When the cold junction temperature is increased by 20°C, then the inversion temperature is __________________.

(a)

200°C

(b)

220°C

(c)

240°C

(d)

110°C

25.

Parts of the energy is used in an electric motor and the remaining part of the energy is dissipated in form of _____________.

(a)

current in the resistors

(b)

heat in the resistor

(c)

voltage in the resistors

(d)

resistance in the resistor

26.

Which of the following produces large Joule heating effect?

(a)

IA current through 2Ω resistor for 3 seconds

(b)

IA current through 3Ω resistor for 2 seconds

(c)

2A current through 1Ω resistor for 2 seconds

(d)

3A current through 1Ω resistor for 1 second

27.

The phase difference between VL and Vc is _________________

(a)

2π

(b)

π/2

(c)

π/4

(d)

28.

Lorentz force generally refers to force experienced by a charge due to combined action of _________________.

(a)

magnetic fields

(b)

electric fields

(c)

electric, magnetic & gravitational fields

(d)

electric and magnetic fields

29.

Consider the motion of a charged particle in a uniform magnetic field directed into the paper. If velocity v of the particle is in the plane of the paper, the charged particle will describe a _____________.

(a)

straight line

(b)

circle

(c)

ellipse

(d)

hyperbola

30.

The algebraic sum of the currents meeting at any junction in the circuit is_______

(a)

infinity

(b)

negative value

(c)

(d)

zero

31.

The unit of temperature coefficient of resistance is_______.

(a)

°C

(b)

°C^-1

(c)

-C^-2

(d)

°C²

32.

The unit henry can also be written as ______________.

(a)

VS A^-1

(b)

Wb A^-1

(c)

Ωs

(d)

all

33.

Melting point of a tungsten filament inside a glass bulb is_________

(a)

3360^o C

(b)

3340^oC

(c)

3380^oC

(d)

3370^oC

34.

The unit of relative permittivity is

(a)

C²N^-1m^-2

(b)

Nm²C^-2

(c)

No unit

(d)

NC^-2 m^-2

35.

The ratio of voltage and current in a dosed circuit is _______________.

(a)

decreases

(b)

increases

(c)

remains constant

(d)

varies

36.

Nichrome wire is used as the heating element because it has _____________.

(a)

low specific resistance

(b)

low melting point

(c)

high specific resistance

(d)

high specific resistance

37.

Resistance between the points A and B in the given figure is

(a)

\(9\Omega \)

(b)

\(2\Omega \quad \)

(c)

\(3\Omega \)

(d)

\(6\Omega \)

38.

The emf of a battery is 3 volts and internal resistance 0.125 \(\Omega \) . The difference of potential at the terminal of battery when connected across an external resistance of 1 \(\Omega \) is ______________.

(a)

1.67 V

(b)

0.67 V

(c)

2.67 V

(d)

3.67 V

39.

An example for a Non-polar molecule is ____________.

(a)

H₂O

(b)

N₂O

(c)

CO₂

(d)

NH₃

40.

During charging a capacitor variation of potential V of the capacitor with time t as shown a

(a)

(b)

(c)

(d)

41.

In a parallel plate capacitor of capacitance C, a metal sheet is inserted between the plates, parallel to them. The thickness of the sheet is half of the separation between the plates. The capacitance now becomes

(a)

(b)

\(\frac{C}{4}\)

(c)

(d)

\(\frac{C}{2}\)

42.

Two charges are kept at a distance in air what should be the relative permittivity of the medium in which the two charges should be kept at the same distance so that they experience half of the force which they experienced in air?

(a)

\(\frac{1}{2}\)

(b)

\(\frac{1}{0.2}\)

(c)

(d)

0.2

43.

The value of constant 'K' in coulomb law is _____________.

(a)

0.9 x 10⁹ Nm² C²

(b)

9 x 10^-9 Nm²C²

(c)

9 x 10⁹ Nm^-2 C^-2

(d)

9 x 10⁹ Nm² C^-2

44.

The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is _____.

(a)

1.00 m A

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

45.

A circular coil with a cross-sectional area of 4 cm² has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm². The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

(a)

7.54 μH

(b)

8.54 μH

(c)

9.54 μH

(d)

10.54 μH

46.

During the propagation of electromagnetic waves in a medium __________________.

(a)

electric energy density is double of the magnetic energy density

(b)

electric energy density is half of the magnetic energy density

(c)

electric energy density is equal to the magnetic energy density

(d)

both electric and magnetic energy densities are zero

47.

In an electromagnetic wave traveling in free space the rms value of the electric field is 3 V m⁻¹. The peak value of the magnetic field is _____.

(a)

1.414 x 10^-8 T

(b)

1.0 x 10^-8 T

(c)

2.828 x 10^-8 T

(d)

2.0 x 10^-8 T

48.

An electric field \(\vec { E } =10x\hat { i } \) exists in a certain region of space. Then the potential difference V = V_o – V_A, where V_o is the potential at the origin and V_A is the potential at x = 2 m is _____.

(a)

10 V

(b)

-20 V

(c)

+20 V

(d)

-10 V

49.

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is ______.

(a)

0.2 Ω

(b)

0.5 Ω

(c)

0.8 Ω

(d)

1.0 Ω

50.

In India electricity is supplied for domestic use at 220 V. It is supplied at 110 V in USA. If the resistance of a 60 W bulb for use in India is R, the resistance of a 60 W bulb for use in USA will be ______.

(a)

(b)

(c)

\(\frac{R}{4}\)

(d)

\(\frac{R}{2}\)

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Answers Key:

Multiple Choice Question

50 x 1 = 50

(d)
All the above

(a)
8 cm

(b)
Enlarged, upright, virtual

(d)
A real, inverted, same-sized image can be formed using a convex mirror

(d)
7.5 cm

(a)
90°

(a)
None

(a)
180 cm

10.

There are two type of Synthesis of nano materials:
(i) Bottom up - Assembling atoms together.
(ii) Top down Breaking down bulk solid.

11.

\(V_{ionisation}=\frac{13.6}{n^2}Z^2 volt\)
\(Z=\sqrt\frac{V\times n^2}{13.6}=\sqrt\frac{122.4 \times I^2}{13.6}=\sqrt{9}=3\)

12.

13.

\(\frac{I}{f}=\left(\frac{\mu_{\mathrm{L}}}{\mu_L}-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\)
When the biconvex lens of glass dipped in liquid, it acts as a plane sheet of glass.
\(\therefore \mathrm{f}=\infty, \frac{1}{\mathrm{f}}=0 \quad \frac{\mu_g}{\mu_{\mathrm{L}}}-1=0 ; \frac{\mu_{\mathrm{s}}}{\mu_{\mathrm{L}}}=1, \mu_{\mathrm{s}}=\mu_{\mathrm{L}}\)

14.

(b)
UV

15.

(b)
5x10⁷

16.

(d)
red

17.

(d)
V_g= V_x= V_m

18.

(b)
charge

19.

(d)
neither depends upon the velocity nor the radius of circular path

20.

21.

22.

(b)
590°C

23.

(b)
remain unchanged

24.

(a)
200°C

25.

(b)
heat in the resistor

26.

(d)
3A current through 1Ω resistor for 1 second

27.

(d)
π

28.

(d)
electric and magnetic fields

29.

(b)
circle

30.

31.

(b)
°C^-1

32.

(d)
all

33.

34.

35.

36.

37.

38.

39.

40.

41.

(a)
2C

42.

(b)
\(\frac{1}{0.2}\)

43.

(d)
9 x 10⁹ Nm² C^-2

44.

45.

\(A_1 =4 \times 10^{-4} \mathrm{~m}^2 \)
\(N_1 =10 \text { turns } \)
\(A_2 =4 \times 10^{-4} \mathrm{~m}^2 \)
\(N_2 =15 \times 10^{-}=1500 \mathrm{turn} / \mathrm{m} \)
\(\phi =B_2 A_2=\left(\mu_0 \mathrm{n}_2 I_2\right) \mathrm{A}_1 \)
\(Where, \mathrm{n}_2=\frac{\mathrm{N}_2}{l}=1500 \mathrm{turn} / \mathrm{m}\)
The mutual Inductance is,
\(M =\frac{N_1 o_{12}}{I_2}=\mu_0 n_2 N_1 A_1 \)
\(=4 \pi \times 10^{-7} \times 1500 \times 10 \times 4 \times 10^{-4} \)
\(=7.54 \times 10^{-6} \mathrm{H}=7.54 \mu \mathrm{H}\)

46.

47.

\(B_o=\frac{E_o}{C}=\frac{\sqrt2E_{rms}}{C}\)
\(B_o=\frac{\sqrt2 \times 3}{3 \times10^8}=1.414 \times10^{-8}T\)

48.

\(\vec {E}\) = 10x\(\hat{i},\) when x = 2 m
\(\vec {E}\) = 10 x 2 x \(\hat{i}\) = 20\(\hat{i}\)
Since, \(E=\frac{-dV}{dx}\therefore V=+20 V\)

49.

I = 0.2 A, R = 10 Ω, E = 2.1 V
\(I=\frac{ɛ}{R+r}\)
\(0.2=\frac{2.1}{10+r}\)
0.2 x (10 + r) = 2.1
2 + 0.2 r = 2.1
0.2 r = 2.1 - 2 = 0.1
Internal resistance, \(r=\frac{0.1}{0.2}=\frac{1}{2}\)
r = 0.5 Ω

50.

\(\mathrm{V}_1 =220 \mathrm{~V}, \quad \mathrm{P}_1=60 \mathrm{~W} \)
\(\mathrm{~V}_{\mathrm{U}} =110 \mathrm{~V}, \mathrm{P}_{\mathrm{U}}=60 \mathrm{~W} \)
\(P =\frac{V^2}{R} \Rightarrow R=\frac{V^2}{P} \)
\(\therefore R_l =\frac{V_I^2}{P_l} \text { Similarly, } \quad \mathrm{R}_U=\frac{V_U^2}{P_U} \)
\(R_l =\frac{220 \times 220}{60} \quad \mathrm{R}_{\mathrm{U}}=\frac{110 \times 110}{60} \)
\(R_I =\frac{48400}{60} \quad R_U=\frac{12100}{60} \)
\(\frac{R_U}{R_l} =\frac{12100}{60} \times \frac{60}{48400}=\frac{1}{4} \)
\(R_U =\frac{R_l}{4}=\frac{R}{4}\)