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

12th Standard

Reg.No. :
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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center 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

2. 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

3. 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

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

(a)

positive

(b)

negative

(c)

zero

(d)

maximum

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

(a)

R

(b)

2R

(c)

$\frac{R}{4}$

(d)

$\frac{R}{2}$

6. 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)

$40\Omega$

7. Relation between current density and drift velocity is_________

(a)

en Vd

(b)

nAeVd

(c)

$\cfrac { n }{ e{ V }_{ d } }$

(d)

$\cfrac { { V }_{ d } }{ ne }$

8. Th ree 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. Th ey are placed in a uniform magnetic fi eld and same electric current is passed through them. Which of the following loop confi guration will experience greater torque ?

(a)

circle

(b)

semi-circle

(c)

square

(d)

all of them

9. 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 solenonid to demagnetize the ferromagnet completely is

(a)

1.00 m A (milli ampere)

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

10. Direction of 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

11. These are behaving like thermistor

(a)

insulators and conductors

(b)

semiconductors and conductors

(c)

insulators and semiconductors

(d)

conductors and alloys

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

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

13. Consider an oscillator which has a charged particle and oscillates about its mean position with a frequency of 300 MHz. Th e wavelength of electromagnetic waves produced by this oscillator is

(a)

1 m

(b)

10 m

(c)

100 m

(d)

1000 m

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

(a)

Hertz

(b)

Maxwell

(c)

Huygens

(d)

Planck

15. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a 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

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

(a)

5

(b)

9

(c)

7

(d)

8

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

(a)

2 mm, 8 mrn, 18 mm

(b)

2 mm, 18 mm, 28 mm

(c)

2 mm, 18 mm, 22 mm

(d)

2 mm, 18 mrn, 58 mm

18. A convex mirror has a focal length f. A real object is placed ata distance Jinfront the pole produces an image at

(a)

infinity

(b)

f

(c)

$\cfrac { f }{ 2 }$

(d)

2f

19. A concave mirror forms an image of sun at a .distance of 12 ern 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

20. 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

21. Einstein's mass energy equivalence is _________

(a)

E = mc2

(b)

E=m0c-mc2

(c)

E=(m0+m2)

(d)

E=m2c4

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

(a)

h

(b)

$\frac{h}{\pi}$

(c)

$\frac{4h}{\pi}$

(d)

$\frac{2h}{\pi}$

23. Energy of an atom at its ground state is ___________

(a)

zero

(b)

maximum

(c)

minimum

(d)

10 eV

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

(a)

B

(b)

Al

(c)

P

(d)

Mg

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

(a)

space

(b)

surface

(c)

ground

(d)

sky