Physics Questions & Answers - Free Online Practice

731.

Calculate the height of the image formed by a pinhole camera of length 12cm used to photograph an object 60cm away from the hole and 70cm high

10 cm

16 cm

5 cm

14 cm

View answer & explanation

Correct answer is D

Magnification = $\frac{\text{Length of camera}}{\text{distance of object from pin hole}}$

m = $\frac{12}{60}$

= 0.2

Also magnification m = $\frac{\text{Height of image}}{\text{Height of object}}$

∴ Height of image = m × height of object

= 0.2 × 70

= 14cm

732.

The S.I unit of moment of a force is

kgm

µm $^{-1}$

View answer & explanation

Correct answer is B

Moment of a force is the product of a force and the perpendicular distance from the line of action of the force
Moment = force × distance
= N × m
= Nm

733.

An element and its isotope only differ in the number of

protons

electrons

ions

neutrons

View answer & explanation

Correct answer is D

Isotopy is due to difference in mass number, what causes the difference is the difference in the number of neutrons present

734.

Which of the following instruments helps to maintain the correct humidity and temperature of a building?

A compressor

A refrigerator

Air blower

Air conditioner

View answer & explanation

Correct answer is D

Compressor is an instrument to supply air or other gas at increased pressure
Refrigerator is an appliance to keep things cold
Air blower is used to release air
Air conditioner is used to remove heat and maintain a stable temperature in an occupied space

735.

Three 3ω resistance are connected in parallel what is the equivalent resistance?

1ω

9ω

3ω

0.33ω

View answer & explanation

Correct answer is A

Resistor connected in a parallel have an equivalence given by
$\frac{1}{\text{Reff}}$ = $\frac{1}{3}$ + $\frac{1}{3}$ + $\frac{1}{3}$

= $\frac{1 + 1 + 1}{3}$ = $\frac{3}{3}$ = 1

Reff = 1ω