Physics 12th Standard Challenge

Question 1

In Young's double-slit experiment, if the distance between the slits is doubled while all other factors remain unchanged, what happens to the fringe width?

Accepted Answer

It becomes half

Answer

It becomes double

Answer

It remains unchanged

Answer

It becomes four times

Question 2

A charged particle enters a uniform magnetic field with velocity perpendicular to the field lines. Which quantity remains unchanged during the motion?

Accepted Answer

Kinetic energy

Answer

Direction of velocity

Answer

Momentum vector

Answer

Angular position

Question 3

Why is the potentiometer considered more accurate than a voltmeter for measuring emf?

Accepted Answer

It works without drawing current from the source at balance point

Answer

It has lower resistance than the cell

Answer

It measures current directly

Answer

It converts emf into magnetic flux

Question 4

In a series LCR circuit at resonance, which statement is correct?

Accepted Answer

Inductive reactance equals capacitive reactance

Answer

Current is minimum and impedance is maximum

Answer

Voltage and current differ in phase by 90 degrees

Answer

Power factor becomes zero

Question 5

Which observation best supports the particle nature of light in Class 12 physics?

Accepted Answer

Emission of electrons in the photoelectric effect

Answer

Interference pattern formation

Answer

Diffraction around obstacles

Answer

Polarization by reflection

Question 6

When an electron jumps from a higher orbit to a lower orbit in a hydrogen atom, the wavelength of emitted radiation depends on the difference in:

Accepted Answer

Total energy of the two levels

Answer

Angular momentum of the orbits

Answer

Potential energies alone

Answer

Orbital radii only

Question 7

In a p-n junction diode under forward bias, the depletion region width primarily:

Accepted Answer

Decreases

Answer

Increases rapidly

Answer

Remains exactly constant

Answer

Becomes zero immediately

Question 8

If the focal length of a convex lens is 20 cm, at what object distance will the image be formed at infinity?

Accepted Answer

20 cm

Answer

10 cm

Answer

30 cm

Answer

40 cm

Question 9

In an ideal transformer, if the secondary has more turns than the primary, the transformer is mainly used to:

Accepted Answer

Step up voltage

Answer

Step down current frequency

Answer

Convert AC to DC

Answer

Reduce magnetic flux to zero

Question 10

A radioactive sample has a decay constant λ. Its mean life is given by:

Accepted Answer

1/λ

Answer

λ

Answer

ln 2 / λ

Answer

2/λ

Physics 12th Standard Challenge

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