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

Published on: 12/10/2020

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

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

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 convex mirror has a focal length f. A real object is placed at a distance Jin front the pole produces an image at ____________.

(a)

infinity

(b)

(c)

\(\cfrac { f }{ 2 } \)

(d)

A point object 0 is placed between two plane mirrors as shown in figure. The distance by mirror M₂ from it are _____________.

(a)

2 mm, 8 mm, 18 mm

(b)

2 mm, 18 mm, 28 mm

(c)

2 mm, 18 mm, 22 mm

(d)

2 mm, 18 mm, 58 mm

Two plane mirrors are at 45° to each other. If an object is placed between them then the number of images will be ________________.

(a)

(b)

(c)

(d)

Einstein's mass energy equivalence is _________

(a)

E = mc²

(b)

E = m₀c - mc²

(c)

E = (m₀+ m²)

(d)

E = m²c⁴

To produce n-type semiconductor which impurity is added into the silicon?

(a)

(b)

(c)

(d)

Radiowaves propagated through the troposphere of the earth are known as __________ waves.

(a)

space

(b)

surface

(c)

ground

(d)

sky

Sodium and copper have work functions of 2.3eV and 4.5eV respectively, then the ratio of the wavelengths is nearest to ___________.

(a)

1: 2

(b)

4: 1

(c)

2: 1

(d)

1: 4

Energy of an atom at its ground state is ___________

(a)

zero

(b)

maximum

(c)

minimum

(d)

10 eV

10.

In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to _____.

(a)

(b)

\(\frac{h}{\pi}\)

(c)

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

(d)

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

11.

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

12.

The existence of E.M. waves was confirmed experimentally by __________________.

(a)

Hertz

(b)

Maxwell

(c)

Huygens

(d)

Planck

13.

These are behaving like thermistor ________________.

(a)

insulators and conductors

(b)

semiconductors and conductors

(c)

insulators and semiconductors

(d)

conductors and alloys

14.

The direction of the magnetic force on a positive charge moving in a magnetic field is given by ________________.

(a)

thumb rule

(b)

left hand rule

(c)

right hand rule

(d)

cork screw rule

15.

Relation between current density and drift velocity is_________

(a)

en V_d

(b)

nAeV_d

(c)

\(\cfrac { n }{ e{ V }_{ d } } \)

(d)

\(\cfrac { { V }_{ d } }{ ne } \)

16.

An unknown resistance is connected in parallel with a 15\(\Omega \) resistance and a 12V battery. What is the value of the unknown resistance if the current in the circuit is 2A?

(a)

\(10\Omega \)

(b)

\(20\Omega \)

(c)

\(30\Omega \)

(d)

\(40\Omega \)

17.

The electric flux is ________ if the electric field lines enter the closed surface.

(a)

positive

(b)

negative

(c)

zero

(d)

maximum

18.

What physical quantities may X and Y represent? [Y represents the first mentioned quantity].

(a)

K.E - velocity of a particle

(b)

pressure - temperature of a given gas (constant volume)

(c)

capacitance - charge to give a constant potential

(d)

potential - capacitance to give a constant charge

19.

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

20.

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

21.

When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

22.

Consider an oscillator which has a charged particle oscillating about its mean position with a frequency of 300 MHz. The wavelength of electromagnetic waves produced by this oscillator is _____.

(a)

1 m

(b)

10 m

(c)

100 m

(d)

1000 m

23.

A parallel plate capacitor stores a charge Q at a voltage V. Suppose the area of the parallel plate capacitor and the distance between the plates are each doubled then which is the quantity that will change?

(a)

Capacitance

(b)

Charge

(c)

Voltage

(d)

Energy density

24.

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

25.

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

25 x 1 = 25

(d)
All the above

(a)
E = mc²

(a)
space

(b)
maximum

10.

\(L=\frac{nh}{2\pi}=\frac{4h}{2\pi}=\frac{2h}{\pi}\)

11.

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

12.

(a)
Hertz

13.

14.

15.

(a)
en V_d

16.

(a)
\(10\Omega \)

17.

(b)
negative

18.

(d)
potential - capacitance to give a constant charge

19.

20.

(a)
Circle

21.

\(\text {emf } e=8 \mathrm{~V} \)
\(d I=I_1-I_0=2-(-2)=4 \mathrm{~A} \)
\(\text {dt }=0.05 \mathrm{~s} \)
\(L=\frac{-e}{d I / d t}=\frac{-8}{4 / 0.05} \)
\(=\frac{-8 \times 0.05}{4}=\frac{-0.40}{4} \)
=-0.1 H
-ve sign indicates that self-induced emf always opposes the current w.r.t. time.

22.

ג = \(\frac{c}{f}=\frac{3 \times10^8}{300 \times 10^6}=1 m\)

23.

Energy density u_E \(=\frac{U}{volume}\)
If A' = 2A d ' = 2d
Then V ' = 2A x 2d = 4Ad = 4V
Then volume would be increased. So, energy density will change.

24.

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

25.

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