NEET Physics 4

Question 1

The work function of a metal is 2 eV. What is the threshold frequency for the photoelectric effect? (h = 6.6 × 10⁻³⁴ J·s)

Accepted Answer

4.83 × 10¹⁴ Hz

Answer

ν₀ = W/h = (2 × 1.6 × 10⁻¹⁹)/(6.6 × 10⁻³⁴) ≈ 4.83 × 10¹⁴ Hz.

Question 2

In a nuclear reaction, ²³⁵U absorbs a neutron and splits into ⁹⁰Kr and ¹⁴³Ba. How many neutrons are released?

Accepted Answer

3

Answer

Mass number conservation: 235+1 = 90+143+n gives n = 3 neutrons released.

Question 3

The half-life of a radioactive element is 10 years. After 40 years, the fraction of the original sample remaining is:

Accepted Answer

1/16

Answer

40 years = 4 half-lives, so the remaining fraction = (1/2)⁴ = 1/16.

Question 4

In a p-n junction diode under forward bias, what happens to the depletion region?

Accepted Answer

It decreases

Answer

Forward bias reduces the potential barrier and narrows the depletion region, allowing current to flow.

Question 5

The output of a NAND gate with inputs A=1 and B=1 is:

Accepted Answer

0

Answer

NAND gate output = NOT(A AND B); when A=B=1, AND=1, so NAND output = 0.

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