Physics Questions & Answers - Free Online Practice

1,986.

A converging lens has a focal length of 5cm. Determine its power

+20.0

+0.2

-20.00

-0.2

View answer & explanation

Correct answer is A

p = \(\frac{100}{f} = \frac{100}{+5} = +20\)

1,987.

The horizontal floor of a water reservoir appears to be 1.0m deep when viewed vertically from above. If the refractive index of water is 1.35, calculate the real depth of the reservoir

2.35m

1.35m

1.00m

0.35m

View answer & explanation

Correct answer is B

n = \(\frac{R.d}{A.d}\)

1.35 = \(\frac{R.d}{1}\)

R.d = 1.35m

1,988.

A converging lens produces an image four times as large as an object placed 25cm from the lens. Calculate its focal length

100cm

33cm

29cm

20cm

View answer & explanation

Correct answer is D

M = \(\frac{v}{u}\)

v = mu = 4 x 25 = 100m

\(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\)

\(\frac{1}{100} + \frac{1}{25} = \frac{1}{f}\)

f = 20cm

1,989.

An object is placed on the principal axis and at the centre of curvature of a concave mirror, the image of the image formed by the mirror is

real and magnified

real and inverted

erect and magnified

erect and virtual

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

1,990.

The image which cannot be formed on a screen is said to be

inverted

erect

real

virtual

View answer & explanation

Correct answer is D

Any image that can be formed on a screen are called real image. Such images are formed by light rays emanating from the object, when reflected and/or refracted by devices such as lenses and mirrors converge at some specific point.

In contrast there are other images which are formed by the rays of light reaching the observer appearing to converge at some point. This happens when the rays reaching the observer are diverging and when the line of these rays are projected backward. Such images, which cannot be formed on a screen, are called virtual image.