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12th Standard Physics English Medium Free Online Test one mark questions with answer key 2020 - Part Seven

Published on: 12/10/2020

12th Standard Physics English Medium Free Online Test one mark questions with answer key 2020 Part Seven

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.

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Std: 12th Standard - Physics

chapter: - Model Question paper

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Questions:

Multiple Choice Question

25 x 1 = 25

Below the threshold frequency, if the intensity of radiation is increased, the emission of photoelectrons _______

(a)

increases

(b)

decreases

(c)

is zero

(d)

is a constant

When the intensity of a light source is increased?

(a)

the number of photons emitted by the source in unit time increases

(b)

more energetic photons are emitted

(c)

faster photons are emitted

(d)

total energy of the photons emitted per unit time decreases.

The particle size of ZnO material is 30 nm. Based on the dimension it is classified as _____.

(a)

Bulk material

(b)

Nanomaterial

(c)

Soft material

(d)

Magnetic material

If a small amount of antimony (Sb) is added to germanium crystal,______.

(a)

it becomes a p-type semiconductor

(b)

the antimony becomes an acceptor atom

(c)

there will be more free electrons than hole in the semiconductor

(d)

its resistance is increased

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

(a)

(b)

(c)

(d)

If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the wave associated with the emitted electron is _____.(Take h = 6.6 x 10^–34 Js)

(a)

< 2.75 ×10⁻⁹m

(b)

≥ 2.75 × 10⁻⁹m

(c)

≤ 2.75 × 10⁻¹²m

(d)

< 2.5 × 10⁻¹⁰m

Light transmitted by Nicol prism is, _____.

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

Stars twinkle due to, ______.

(a)

reflection

(b)

total internal reflection

(c)

refraction

(d)

polarisation

The phase difference between electric and magnetic field vectors in the electromagnetic waves?

(a)

\(\frac{\pi}{4}\)

(b)

\(\frac{\pi}{2}\)

(c)

\(\pi\)

(d)

zero

10.

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

11.

The instantaneous current in an AC circuit containing a pure inductor is i = I_o sinωt, The instantaneous emf is ___________________.

(a)

e = E_osin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)

(b)

e = E_osin\(\left( \omega t-\frac { \pi }{ 2 } \right) \)

(c)

e=E_osin(ωt - π)

(d)

e = E_osin

12.

In a single phase dynamo, the direction of the induced current is given by __________

(a)

Faraday's laws

(b)

Maxwell's equations

(c)

Einstein's equation

(d)

Fleming's right hand rule

13.

In a carbon resistor, the third ring represents___________

(a)

powers of zeros

(b)

powers of ten

(c)

ten

(d)

infinity

14.

Which current- time graph represents the steady movement of short magnet through a coil XY?

(a)

(b)

(c)

(d)

15.

A Gaussian surface in the figure is shown by dotted line. The electric field on the surface will be

(a)

due to q₁ and q₂ only

(b)

due to q₂ only

(c)

zero

(d)

due to all

16.

Charge Q on a capacitor varies with voltage V as shown in graph, where Q is along X-axis and V along Y-axis. The area of triangle OAB represents

(a)

capacitance

(b)

capacitive reactance

(c)

magnetic field between the plates

(d)

energy stored in the capacitor

17.

The electric flux through a surface will be minimum when the angle between E and A is

(a)

90°

(b)

60°

(c)

0°

(d)

45°

18.

A non-conducting material which has no free electrons is called

(a)

capacitor

(b)

Dielectric

(c)

conductor

(d)

Inductor

19.

An electron moves in a straight line inside a charged parallel plate capacitor of uniform charge density σ. The time taken by the electron to cross the parallel plate capacitor undeflected when the plates of the capacitor are kept under constant magnetic field of induction \((\vec{B})\) is

(a)

\({ \varepsilon }_{ ° }\frac { elB }{ \sigma } \)

(b)

\({ \varepsilon }_{ ° }\frac { lB }{ \sigma {l} } \)

(c)

\({ \varepsilon }_{ ° }\frac { lB }{ {e}\sigma } \)

(d)

\({ \varepsilon }_{ ° }\frac { lB }{ \sigma } \)

20.

A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is

(a)

1.2

(b)

0.83

(c)

0.12

(d)

0.9

21.

The flux linked with a coil at any instant t is given by \(\Phi\)_B = 10t²− 50t + 250. The induced emf at t = 3s is

(a)

−190 V

(b)

−10 V

(c)

10 V

(d)

190 V

22.

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

23.

Two identical conducting balls having positive charges q₁ and q₂ are separated by a centre to centre distance r. If they are made to touch each other and then separated to the same distance, the force between them will be _____.

(a)

less than before

(b)

same as before

(c)

more than before

(d)

zero

24.

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

25.

A wire connected to a power supply of 230 V has power dissipation P₁. Suppose the wire is cut into two equal pieces and connected parallel to the same power supply. In this case power dissipation is P₂. The ratio \(\frac{P_2}{P_1}\) is ______.

(a)

(b)

(c)

(d)

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Answers Key:

Multiple Choice Question

25 x 1 = 25

(a)
the number of photons emitted by the source in unit time increases

Size of the particle is between
1-100 nm - Nano.
Size of the particle is greater
than-100 nm - Bulk.

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

(b)
≥ 2.75 × 10⁻⁹m

(d)
zero

10.

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

11.

(a)
e = E_osin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)

12.

(d)
Fleming's right hand rule

13.

14.

15.

(d)
due to all

16.

(d)
energy stored in the capacitor

17.

(a)
90°

18.

(b)
Dielectric

19.

Electric field between the plates \(= \frac{σ}{ε_0}\)
Electric force on an electron \(= e\frac{σ}{ε_0}\)
Magnetic force on an electron, F = BIl
But, \(I= \frac{e}{t}\)
∵Electron moves in a straight line. So,
E_F= M_F
\(e\frac{σ}{ε_0}=B(\frac{e}{t})l\)
\(\therefore t = ε_0\frac{lB}{σ}\)

20.

\(\mathrm{V}_{\mathrm{P}}=220 \mathrm{~V}, \mathrm{~V}_{\mathrm{s}}=11 \mathrm{~V} \)
\(\mathrm{I}_{\mathrm{P}}=6 \mathrm{~A}, \mathrm{I}_{\mathrm{s}}=100 \mathrm{~A} . \)
\(\text {Efficiency }=\frac{\mathrm{V}_{\mathrm{s}} \mathrm{I}_{\mathrm{s}}}{\mathrm{V}_{\mathrm{P}} \mathrm{I}_{\mathrm{P}}} \)
\(=\frac{11 \times 100}{220 \times 6}=\frac{1100}{220 \times 6}=\frac{5}{6}=0.83\)

21.

\(\phi_B =10 t^2-50 t+250 \)
\(e =\frac{-d \phi_B}{d t} \)
\(=\frac{-d}{d t}\left(10 t^2-50 t+250\right) \)
=-(20 t - 50)
=-20 t + 50
When, t = 3 s, e =-20(3) + 50 = -60 + 50
e = -10V

22.

23.

Force ∝ charge
After the separation, the magnitude of charge will be increased. So the force will be more than before.

24.

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

25.

\(\mathrm{V}=230 \mathrm{~V} \)
\(P=\frac{V^2}{R} \text { since } \mathrm{V} \text { is same } \mathrm{P} \propto \frac{1}{R} \)
\(\frac{1}{R_2}=\frac{1}{\frac{R_1}{2}}+\frac{1}{\frac{R_1}{2}}=\frac{2}{R_1}+\frac{2}{R_1}=\frac{2+2}{R_1} \)
\(\frac{1}{R_2}=\frac{4}{R_1} \)
\(\therefore R_2=\frac{R_1}{4} \)
\(R_1=4 R_2 \)
\(\therefore \frac{P_2}{P_1}=\frac{R_1}{R_2}=\frac{4 R_2}{R_2}=4\)