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WAEC Physics Past Questions & Answers - Page 16

76.

An object is placed at different distances, u, from a converging lens of focal length, 15.0cm. For what value of u does the lens act as a microscope?

A.

u = 15cm only

B.

u = 30cm only

C.

M < 15cm only

D.

u > 30cm only

Correct answer is D

Objects at a distance greater than two times of the focal length produces a real image, inverted and diminished in size.

→ 2 * 15 = 30cm

: At >30cm this is applicable  

77.

A freely suspended compass needle on the earth's surface settles in a plane called----------

A.

geographic meridian

B.

magnetic meridian

C.

magnetic declination

D.

isoganals

Correct answer is B

The magnetic meridian is an equivalent imaginary line connecting the magnetic south and north poles and can be taken as the horizontal component of magnetic force lines along the surface of the earth. Therefore, a compass needle will be parallel to the magnetic meridian

78.

The efficiency of a wheel and axle is 100% and the ratio of their radii is 5:1. calculate the effort required to lift a load of mass 20kg using this machine, [g = 10 m s2]

A.

20N

B.

25N

C.

40N

D.

100N

Correct answer is C

VR = 5:1 or 5

Load = 20kg or 200N

MA = 200E

Efficiency% = MAVR100

100% = 2005E100

5E = 200

E = 40

79.

Which of the following descriptions of the image formed by a plane mirror is not correct. the image is----

A.

erect and of the same size as the object

B.

laterally inverted and of the same size as the object

C.

erect and bigger than the object

D.

virtual and if the same size

Correct answer is C

Images formed by plane mirrors are virtual, upright, left-right reversed, the same distance from the mirror as the object's distance, and the same size as the object

80.

An example of a mechanical wave is---------

A.

water waves

B.

radio waves

C.

x-rays

D.

light rays

Correct answer is A

A mechanical wave is a wave that is an oscillation of matter. 

A sound wave is a mechanical wave that propagates along or through a medium by particle-to-particle interaction.

Sound waves, water waves and seismic waves are some examples of mechanical waves mechanical wave.