WAEC Physics Past Questions & Answers - Page 81

401.

The minimum energy required to cause photoelectric emission when the surface of a metal is irradiated with electromagnetic radiation of suitable frequency is called

A.

critical energy

B.

ionization energy

C.

work function

D.

planck's constant

Correct answer is C

No explanation has been provided for this answer.

402.

The work function of a metal is 2.56 x 10-19J. Calculate the frequency of a photon whose energy is required to eject from the metal an electron with kinetic energy of 3.0ev. [1 eV = 1.6 x 10-19J, h = 6.6 x 10-34Js]

A.

5.56 x 1019Hz

B.

1.66 x 1019Hz

C.

1.12 x 1015Hz

D.

8.42 x 1014Hz

Correct answer is C

F = \(\frac{K.E + Wo}{h}\)

= \(\frac{3.0 \times 1.6 \times 10^{-19} + 2.56 \times 106{-19}}{6.6 \times 106{-34}}\)

- 1.12 x 10-15HZ

403.

A coil of inductance 0.12 H and resistance 4\(\Omega\), is connected across a 240V, 50Hz supply. Calculate the current through it. [\(\pi\) = 3.142]

A.

6.3A

B.

33.3A

C.

37.2A

D.

40.0A

Correct answer is A

XL = \(2\pi f L\)

= = 2 x 3.142 x 50 x 0.12

= 37.68\(\Omega\)

Z = \(\sqrt{R^2 + X_L^2} = \sqrt{4^2 + 37.68^2}\)

I = \(\frac{V}{z} = \frac{240}{37.89}\)

= 6.3A

404.

Which of the following devices does not makes use of eddy current for its action? A/An

A.

galvanometer

B.

speedometer

C.

induction furnace

D.

speedometer

Correct answer is A

No explanation has been provided for this answer.

405.

The capacitance of parallel plates capacitors varies

A.

inversely as the square of the distance between the plates

B.

directly as the square of the distance between the plates

C.

inversely as the distance between the plates

D.

directly as the distance between the plate

Correct answer is A

No explanation has been provided for this answer.