Physics Questions & Answers - Free Online Practice

2,166.

A cell of e.m.f. 1.5v is connected in series with a resistor of 3\(\Omega\). A high resistance voltmeter connected across the cell registers only 0.9v. Calculate the internal resistance of the cell

5.0\(\Omega\)

4.5\(\Omega\)

2.4\(\Omega\)

2.0\(\Omega\)

1.8\(\Omega\)

View answer & explanation

Correct answer is D

E.M.F (E) = 1.5v, Internal Resistance (r) = ?, Potential Difference (V) = 0.9v, Load resistance (R) = 3Ω,

Current (I) = V / R = 0.9 / 3 = 0.3A

USING : E = I ( R + r )

r = (E / I) - R = (1.5 / 0.3) - 3

r = 5 - 3

r = 2Ω,

2,167.

In the electrical method of magnetisation, the polarity of the magnet depends on the

amount of current passed

direction of current

magnetic material used

size of the magnetic material

orientation of the magnetic material in space

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Correct answer is B

No explanation has been provided for this answer.

2,168.

The gravitational force of the moon is one-sixth that of the earth. If a body weighs 6.0N on the moon. Calculate its weight on the earth

36.0N

12.0N

6.0N

2.0N

1.0N

View answer & explanation

Correct answer is A

\(\frac{1}{6}F_E = F_{MOON}\)

F_E = R = 6F_m

= 6 x 6 = 36N

2,169.

An electromagnetic wave of frequency 5.0 x 10¹⁴Hz, is incident on the surface of water of refractive index \(\frac{4}{3}\). Taking the speed of the wave in air as 3.0 x 10⁸ms^-1, calculate the wavelength of the wave in water.

2.2 x 10^-6m

1.7 x 10^-7m

8.0 x 10^-7m

6.0 x 10^-7m

4.5 x 10^-7m

View answer & explanation

Correct answer is E

\(_an_w = \frac{\lambda_a}{\lambda_w}\)

\(\frac{4}{3} = \frac{\lambda_a}{\lambda}\)

\(\lambda_w = \frac{v}{f}\)

= \(\frac{3.0 \times 10^8}{5.0 \times 10^{14}} = 0.6 \times 10^{-6}\)

\(\lambda_w = \frac{3}{4} \lambda_a = \frac{3}{4} \times 0.6 \times 10^{-6}\)

= 4.5 x 10^-7m