Tag: physics

Questions Related to physics

The relation between $u,\,v\;and\;f$ for a mirror is given by

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. $f=\displaystyle\frac{u\times v}{u-v}$

  2. $f=\displaystyle\frac{2u\times v}{u+v}$

  3. $f=\displaystyle\frac{u\times v}{u+v}$

  4. $f=\displaystyle\frac{u-v}{u+v}$

Show answer
Correct Option: C
Explanation:

The relation between $u,\,v\;and\;f$ for a mirror is given by $f=\displaystyle\frac{u\times v}{u+v}$

Choose the correct relation between $u,\,v\;and\;r$ for a spherical mirror, where $r$ is radius of curvature.

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. $r=\displaystyle\frac{2uv}{u+v}$

  2. $r=\displaystyle\frac{2}{u+v}$

  3. $r=\displaystyle\frac{2(u+v)}{(uv)}$

  4. $r=\displaystyle\frac{2uv}{u-v}$

Show answer
Correct Option: A
Explanation:

The relation between $u,\,v\;and\;f$ for a mirror is given by $f=\displaystyle\frac{u\times v}{u+v}$

so $r=\displaystyle\frac{2u\times v}{u+v}$

The unit of magnification is :

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. $m$

  2. $m^2$

  3. $m^{-1}$

  4. it has no units

Show answer
Correct Option: D
Explanation:

Magnification is a ratio of lengths, hence it has no units

The ratio of the size of the image to the size of the object is known as :

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. the focal plane

  2. the transformation ratio

  3. the efficiency

  4. the magnification ratio

Show answer
Correct Option: D
Explanation:

magnification ratio is given as:

 size or height of image/ size or height of object
substituted with proper sign convention.

An object is placed at a distance of 40 cm in front of a concave mirror of focal length 20 cm. Determine the ratio of the size of the image and the size of object

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. 2:1

  2. 1:2

  3. 1:1

  4. 4:1

Show answer
Correct Option: C
Explanation:

Since focal length of concave mirror given is 20cm l. Object is at 40cm distance which means it is at centre of curvature. hence, image will be formed of same size and at centre focus only but real and inverted.

Linear magnification is

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. Positive for an inverted image

  2. Negative for an erect image

  3. Zero for an inverted image

  4. Negative for an inverted image

Show answer
Correct Option: D
Explanation:

Linear magnification is given as Image size/ Object size

For calculations of magnification, values of image size and object size are taken with proper sign convention. 
For an inverted image, the image size is taken as negative and hence magnification is negative.

Distances measured below the principal axis are taken as ........

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. Positive

  2. Negative

  3. None

  4. Both

Show answer
Correct Option: B
Explanation:

According to the sign convention followed for mirrors and for lenses, the distances measured above the principal axis are taken as positive and the distances measured below the principal axis are taken as negative.

Hence, the correct answer is OPTION B.

State whether true or false : 

The magnification produced by a spherical mirror is the ratio of the height of the image to the height of the object.

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The magnification is the ratio of height of the image to height of the object. The image is smaller than the object, the magnification will be less than 1. If the image if upside down (inverted) then magnification will be negative.

A concave mirror forms an erect image of an object placed at a distance of 10 cm from it. The size of the image is double that of the object. Where is the image formed?

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. 20 cm behind the mirror 

  2. 20 cm in front of the mirror

  3. 40 cm behind the mirror

  4. 40 cm in front of the mirror

Show answer
Correct Option: A
Explanation:

Since the image is erect , so the magnification ratio must be positive .


$m=2$

also $u=-10cm$

so $m=-\dfrac{v}{u}$

$2=-\dfrac{v}{-10}$ 

$v=20cm$

So the image is virtual and 20 cm from mirror on the other side of the object.

A dentist wants a small mirror that when placed $2$cm from a tooth, will produce $3\times$ upright image. What kind of mirror must be used and what must its focal length be?

physics reflection of light in spherical mirrors sign convention for mirrors sign convention for spherical mirrors sign convention for the measurement of distances

  1. Concave mirror, $3.04$ cm

  2. Concave mirror, $1.5$ cm

  3. Convex mirror, $3.0$ cm

  4. Convex mirror, $1.5$cm

Show answer
Correct Option: C
Explanation:

$m=+\dfrac{v}{u}=\dfrac{+f}{u-f}$
$3=\dfrac{+f}{+2+f}\Rightarrow f=3cm$.