Physics Flashcards

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)

Answer: 4.83 × 10¹⁴ Hz

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

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

Answer: 3

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

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

Answer: 1/16

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

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

Answer: It decreases

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

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

Answer: 0

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

The binding energy per nucleon is highest for which element?

Answer: Iron (Fe-56)

Fe-56 has the highest binding energy per nucleon (~8.8 MeV), making it the most stable nucleus.

The de Broglie wavelength of an electron accelerated through a potential difference V is proportional to:

Answer: 1/√V

Since λ = h/mv and kinetic energy eV = ½mv², we get λ = h/√(2meV), so λ ∝ 1/√V.