12th standard Physics full portion important One Mark Questions - 2020

Download Tamil Nadu 12th Standard Physics question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.

Questions:

Multiple Choice Question

44 x 1 = 44

A short liner object of length I lie along the axis of a concave mirror of focal length f at a distance μ₁ from the pole of the mirror. The size of the image is approximately equal to _____________.

(a)

\(1\left| \cfrac { u-f }{ f } \right| ^{ \frac { 1 }{ 2 } }\)

(b)

\(1\left| \cfrac { \mu -f }{ f } \right| ^{ 2 }\)

(c)

\(1\left| \cfrac { f }{ \mu -f } \right| ^{ \frac { 1 }{ 2 } }\)

(d)

\(1\left| \cfrac { f }{ \mu -f } \right| ^{ 2 }\)

For the largest distance of the image from a concave mirror of focal length 10 cm, the object should be kept at ______________.

(a)

10 cm

(b)

Infinite

(c)

40 cm

(d)

60 cm

For a given photo sensitive surface the ratio of stopping potential for three different incident frequencies is ______________.

(a)

1: 2 : 3

(b)

1: 4: 9

(c)

1: 1 : 1

(d)

\(\sqrt { 1 } :\sqrt { 2 } :\sqrt { 3 } \)

Plasma etching and chemical vapour deposition are synthesized by ____________

(a)

Bottom - up approach

(b)

Top - down approach

(c)

Bottom - down approach

(d)

Top - up approach

Best example for applications of nanotechnology is ______________.

(a)

Chemical industry

(b)

Engineering

(c)

medicine

(d)

all of these

In PNP transistors, the direction of conventional current, when emitter-base junction is forward-biased is from __________

(a)

base to emitter

(b)

emitter to base

(c)

collector to base

(d)

base to collector

The electron gun assembly contains a _________.

(a)

CRO

(b)

cathode and a control grid

(c)

multimeter

(d)

power supply

In an electron microscope, the doughnut shaped electromagnet is called as _______

(a)

accelerator

(b)

electron gun

(c)

projector

(d)

condenser magnetic lens

The component of the modulated wave, which has a greater frequency than that of the carrier is called __________.

(a)

upper side band

(b)

middle side band

(c)

lower side band

(d)

stoke's band

10.

Zener diode is used as _______

(a)

full wave rectifier

(b)

Amplifier

(c)

A.C. voltage regulator

(d)

D.C. voltage regulator

11.

A good _____ slows down neutrons by elastic collisions and it does not remove them by absorption.

(a)

fuel

(b)

moderator

(c)

coolant

(d)

control rod

12.

If R is Rydberg's constant, the minimum wavelength of hydrogen spectrum is _____________.

(a)

1/R

(b)

R/4

(c)

4/R

(d)

13.

The technology used for stopping the brain from processing pain is _____.

(a)

Precision medicine

(b)

Wireless brain sensor

(c)

Virtual reality

(d)

Radiology

14.

“Sky wax” is an application of nano product in the field of _____.

(a)

Medicine

(b)

Textile

(c)

Sports

(d)

Automotive industry

15.

The frequency range of 3 MHz to 30 MHz is used for ______.

(a)

Ground wave propagation

(b)

Space wave propagation

(c)

Sky wave propagation

(d)

Satellite communication

16.

The output transducer of the communication system converts the radio signal into ________.

(a)

Sound

(b)

Mechanical energy

(c)

Kinetic energy

(d)

None of the above

17.

If a positive half-wave rectified voltage is fed to a load resistor, for which part of a cycle there will be current flow through the load?

(a)

0⁰–90⁰

(b)

90⁰–180⁰

(c)

0⁰–180⁰

(d)

0⁰–360⁰

18.

The barrier potential of a silicon diode is approximately, ______.

(a)

0.7 V

(b)

0.3 V

(c)

2.0 V

(d)

2.2 V

19.

If the nuclear radius of ²⁷Al is 3.6 fermi, the approximate nuclear radius of ⁶⁴Cu, in femi is _____.

(a)

2:4

(b)

1.2

(c)

4.8

(d)

3.6

20.

In J.J. Thomson e/m experiment, electrons are accelerated through 2.6 kV enter the region of crossed electric field and magnetic field of strength 3.0 x 10⁴ Vm^-1 and 1.0 x 10^-3 T, respectively, and pass through it and undeflected, then the specific charge is _____.

(a)

1.6 × 10¹⁰ C kg^–1

(b)

1.7 × 10¹¹ Ckg^–1

(c)

1.5 × 10¹¹ Ckg^–1

(d)

1.8 × 10¹¹ Ckg^–1

21.

If the mean wavelength of light from sun is taken as 550 nm and its mean power as 3.8 x 10²⁶W, then the number of photons emitted per second from the sun is of the order of _____.

(a)

10⁴⁵

(b)

10⁴²

(c)

10⁵⁴

(d)

10⁵¹

22.

The wavelength λ_eof an electron and λ_p of a photon of same energy E are related by _____.

(a)

λ_p ∝ λ_e

(b)

\({ \lambda }_{ p }∝ \sqrt { { \lambda }_{ e } } \)

(c)

\({ \lambda }_{ p }∝ \frac { 1 }{ \sqrt { { \lambda }_{ e } } } \)

(d)

\({ \lambda }_{ p }∝ { \lambda }_{ e }^{ 2 }\)

23.

Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are _____.

(a)

5I and I

(b)

5I and 3I

(c)

9I and I

(d)

9I and 3I

24.

For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is, ______.

(a)

30^o

(b)

45^o

(c)

60^o

(d)

90^o

25.

______ radiations are used in destroying bacteria.

(a)

(b)

(c)

X-ray

(d)

Gamma rays

26.

The wavelength of electromagnetic wave produced by Hertz experiment was _____________.

(a)

6mm

(b)

60m

(c)

6000 mm

(d)

60 cm

27.

The heating element that does not oxidize readily in an alloy of metals made of ______

(a)

Nickel and Iron

(b)

Nickel and Chromium

(c)

Copper and Magnanin

(d)

Nickel and Copper

28.

Two parallel conductors of length 10m carrying same current separated by 20cm in air experiences a force of 0.9N. then the current in each conductor is ________________.

(a)

30A

(b)

300nA

(c)

300\(\sqrt { 2 } \)A

(d)

300A

29.

In an LCR series a.c, circuit, the phase difference between current and voltage is 60°. If the net reactance of the circuit is 17.32Ω, the value of the resistance is ______________.

(a)

30Ω

(b)

17.32 Ω

(c)

10 Ω

(d)

1.732 Ω

30.

The transition temperature of mercury is________

(a)

4.2°C

(b)

4.2 K

(c)

2.4°C

(d)

2.4K

31.

Transformer works on _____________.

(a)

AC only

(b)

DC only

(c)

both AC and DC

(d)

AC more effectively than DC

32.

The resistance of the wire varies inversely as _________________.

(a)

area of cross section

(b)

resistivity

(c)

length

(d)

temperature

33.

Electrostatics deals with the _________

(a)

charges in motion

(b)

static electric charges

(c)

charges through conductors

(d)

accelerated charges

34.

At Infinity (i.e r = ∞), the electrostatic potential (V) is

(a)

∞

(b)

maximum

(c)

minimum

(d)

Zero

35.

A non-conducting charged ring carrying a charge of q, mass m and radius r is rotated about its axis with constant angular speed ω. Find the ratio of its magnetic moment with angular momentum is _____.

(a)

\(\\ \frac { q }{ m } \)

(b)

\(\\ \frac { 2q }{ m } \)

(c)

\(\\ \frac { q }{ 2m } \)

(d)

\(\\ \frac { q }{ 4m } \)

36.

Three wires of equal lengths are bent in the form of loops. One of the loops is circle, another is a semi-circle and the third one is a square. They are placed in a uniform magnetic field and same electric current is passed through them. Which of the following loop configuration will experience greater torque?

(a)

Circle

(b)

Semi-circle

(c)

Square

(d)

All of them

37.

In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is

(a)

\(\frac{Q}{2}\)

(b)

\(\frac{Q}{\sqrt3}\)

(c)

\(\frac{Q}{\sqrt2}\)

(d)

38.

In an electrical circuit, R, L, C, and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is \(\frac{\pi}{3}\). Instead, if C is removed from the circuit, the phase difference is again \(\frac{\pi}{3}\). The power factor of the circuit is

(a)

1/2

(b)

1/\(\sqrt2\)

(c)

(d)

\(\sqrt3\)/2

39.

The electric and magnetic fields of an electromagnetic wave are _____.

(a)

in phase and perpendicular to each other

(b)

out of phase and not perpendicular to each other

(c)

in phase and not perpendicular to each other

(d)

out of phase and perpendicular to each other

40.

A radiation of energy E falls normally on a perfectly reflecting surface. Th e momentum transferred to the surface __________________.

(a)

\(\frac{E}{c}\)

(b)

2\(\frac{E}{c}\)

(c)

(d)

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

41.

If voltage applied on a capacitor is increased from V to 2V, choose the correct conclusion.

(a)

Q remains the same, C is doubled

(b)

Q is doubled, C doubled

(c)

C remains same, Q doubled

(d)

Both Q and C remain same

42.

The total electric flux for the following closed surface which is kept inside water

(a)

\(\frac { 80q }{ { \varepsilon }_{ 0 } } \)

(b)

\(\frac { q }{ { 40\varepsilon }_{ 0 } } \)

(c)

\(\frac { q }{ { 80\varepsilon }_{ 0 } } \)

(d)

\(\frac { q }{ { 160\varepsilon }_{ 0 } } \)

43.

The temperature coefficient of resistance of a wire is 0.00125 per °C. At 20°C, its resistance is 1 Ω. The resistance of the wire will be 2 Ω at ______.

(a)

800 °C

(b)

700 °C

(c)

850 °C

(d)

820 °C

44.

The following graph shows current versus voltage values of some unknown conductor. What is the resistance of this conductor?

(a)

2 ohm

(b)

4 ohm

(c)

8 ohm

(d)

1 ohm

Visit QB365-SLMS - https://www.qb365.in/slms/

Answers Key:

Multiple Choice Question

44 x 1 = 44

(d)
\(1\left| \cfrac { f }{ \mu -f } \right| ^{ 2 }\)

(a)
10 cm

(d)
\(\sqrt { 1 } :\sqrt { 2 } :\sqrt { 3 } \)

(a)
Bottom - up approach

(d)
all of these

(b)
emitter to base

(b)
cathode and a control grid

(d)
condenser magnetic lens

(a)
upper side band

10.

(d)
D.C. voltage regulator

11.

(b)
moderator

12.

For minimum wavelength \(\mathrm{n}=1, \mathrm{~m}=\infty\)
\(\therefore \bar{v}=\frac{1}{\lambda}=R \Rightarrow \lambda=\frac{1}{\mathrm{R}}\)

13.

Medical virtual reality is effectively used to stop the brain from processing pain and cure soreness.

14.

15.

Ground wave propagation: frequency less than 2 MHz
Sky wave propagation: 3 to 30 MHz
Space wave propagation: Above 30 MHz to 400 GHz
Satellite communication: uplink communication 6 GHz band downlink communication 4 GHz band

16.

(a)
Sound

17.

18.

(a)
0.7 V

19.

\(r \propto A^{\frac{1}{3}} \)
\(\frac{r_{\mathrm{Cu}}}{\mathrm{r}_{\mathrm{Al}}}=\frac{\mathrm{A}_{\mathrm{Cu}}^\frac{1}{3}}{\mathrm{~A}_{\mathrm{Al}}^{\frac{1}{3}}}=\frac{4}{3} \)
\(\mathrm{r}_{\mathrm{Cu}}=\frac{4}{3} \times 3.6 \mathrm{~F}=4.8 \mathrm{~F}\)

20.

(b)
1.7 × 10¹¹ Ckg^–1

21.

\(\mathrm{P} =\frac{\mathrm{n}}{\mathrm{t}} \frac{\mathrm{hc}}{\lambda} \)
\(\frac{\mathrm{n}}{\mathrm{t}} =\frac{\mathrm{P} \lambda}{\mathrm{hc}} \)
\(\frac{\mathrm{n}}{\mathrm{t}} =\frac{3.8 \times 10^{26} \times 550 \times 10^{-9}}{6.6 \times 10^{-3} \times 3 \times 10^8}=1 \times 10^{-15}\)

22.

\(\mathrm{E}_{\mathrm{p}} =\frac{\mathrm{hc}}{\lambda_{\mathrm{p}}} \)
\(\mathrm{E}_{\mathrm{e}} =\frac{\mathrm{h}^2}{2 \mathrm{~m} \lambda_{\mathrm{e}}^2} \)
\(\frac{\mathrm{hc}}{\lambda_{\mathrm{p}}} =\frac{\mathrm{h}^2}{2 \mathrm{~m} \lambda_{\mathrm{e}}^2} \)
\(\lambda_{\mathrm{p}} \propto \lambda_{\mathrm{e}}^{{ }^2}\)

23.

I = l₁ + l₂ + 2\(\sqrt{I_1I_2}\)cos θ
If cos θ = cos 0 = l, I is max
= I+ 4I + 2\(\sqrt{41^2}\) cos 0
= 5I + 4I = 91
If cos π = -1, I is min
I_min = I + 4I + 2\(\sqrt{41^2}\) cos π
= 5I + 4I(-1)
= 5I + 4I = I
(I_max, I_min)= (9I, I)

24.

(a)
30^o

25.

(a)
UV

26.

27.

(b)
Nickel and Chromium

28.

(d)
300A

29.

30.

(b)
4.2 K

31.

(a)
AC only

32.

(a)
area of cross section

33.

(b)
static electric charges

34.

(d)
Zero

35.

Magnetic moment,
μ = IA
Angular momentum,
L = Iω
Ratio \(\frac{p_m}{L}=\frac{(q/T)\pi r^2}{mr^2\omega}=\frac{q}{2m}\)

36.

(a)
Circle

37.

\(Q_{midpoint}=\frac{Q}{\sqrt{1^2+1^2}}=\frac{Q}{\sqrt2}\)

38.

\(\Phi = \frac{\pi}{3}-\frac{\pi}{3}=0 \)
Power factor = cosФ = cos 0 = 1

39.

(a)
in phase and perpendicular to each other

40.

(b)
2\(\frac{E}{c}\)

41.

If voltage is increased from V to 2 V
Then Q₁ = CV
Q₂ = C(2 V) = 2 CV
∴ Q is doubled and C remains same

42.

\(Φ=\frac { q_{net} }{ { \varepsilon }_{ 0 } } \)
q_net = - q + q + 2q = 2q
Relative permittivity of water = 80
\(\therefore Φ=\frac { q }{{ \varepsilon }_{ r } { \varepsilon }_{ 0 } } \)
\(=\frac{2q}{{ 80 \times \varepsilon }_{ 0 }}=\frac{q}{{ 40 \varepsilon }_{ 0 }}\)

43.

R_t = R_o [1 + α(T₂ - T₁)
2 = 1[1 + 0.00125(T₂ - 293)
I = 5/4 x 10^-3(T₂ - 293)
T₂ = 1093 K
T₂ = 820 ^oC