Tag: physics

Questions Related to physics

The suns diameter is $1.4\times { 10 }^{ 9 }m$ and its distance from the earth is ${ 10 }^{ 11 }m$. The diameter of its image, formed by a convex mirror of focal length 2m will

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. 0.7 cm

  2. 1.4 cm

  3. 2.8 cm

  4. 10 cm

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Correct Option: C

The distance of real object when a concave mirror produces a real image of magnification $'m'$ is ($f$ is focal length)

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. $\left(\frac{m - 1}{m}\right) f$

  2. $\left(\frac{m + 1}{m}\right) f$

  3. $(m-1)f$

  4. $(m+1)f$

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Correct Option: D

Converging rays are incident on a convex spherical mirror so that their extensions intersect  $30 cm$  behind the mirror on the optical axis. The reflected rays form a diverging beam, so that their extensions intersect the optical axis  $1.2 m$  from the mirror. The focal length of the mirror is

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. $40{ cm }$

  2. $60{ cm }$

  3. $30{ cm }$

  4. $24{ cm }$

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Correct Option: A

Magnification produced by a rear view mirror fitted in vehicles

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. is less than one

  2. is more than one

  3. is equal to one

  4. can be more than or less than one depending upon the position of the object in front of it.

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Correct Option: A

A concave mirror of radius of curvature 40 cm forms an image of an object placed on the principal axis at a distance 45 cm in front of it. Now if the system (including object) is completely immersed in water $(\mu=1.33)$, then:

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. the image will shift towards the mirror.

  2. the magnification will reduce.

  3. the image will shift away from the mirror and magnification will increase.

  4. the position of the image and magnification will not change.

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Correct Option: D
Explanation:

Mirror operates on the principle of Laws of reflection. 

Therefore, focal length does not depend upon the medium and object distance is also unchanged, so their will be no change in the image distance, correspondingly magnification will also remain unchanged.

The radius of curvature for a plane mirror is

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. Positive

  2. Negative

  3. Infinite

  4. None of these

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Correct Option: C
Explanation:

Plane mirrors are not curved.

The distance at which an object should be placed in front of a convex lens of focal length 10 cm to obtain a real image double the size of object will be:

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. 30 cm

  2. 15 cm

  3. 5 cm

  4. 10 cm

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Correct Option: B
Explanation:

Convex lens gives the real and double-sized image when the object is placed exactly between the focus and radius of curvature.
We have, $\displaystyle \frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$m = \displaystyle \frac{v}{u} = 2$ or $v = 2u$


$\therefore \displaystyle \frac{1}{f} = \frac{1}{2u} - \frac{1}{-u} = \frac{1}{2u} + \frac{1}{u} = \frac{3}{2u}$

or $\displaystyle \frac{1}{10} = \frac{3}{2u}$ or $u = 15 cm$

The focal length of a convex mirror is $10cm$. Its radius of curvature will be:

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. $5cm$

  2. $10cm$

  3. $20cm$

  4. $30cm$

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Correct Option: C
Explanation:

The relation between focal length and Radius of curvature is,

$R=2f$
Here focal length is 10cm so,
$R=2\times 10 = 20cm$

An object is placed at the centre of curvature of a concave mirror of radius of curvature $20$cm. The nature and position of the image shall be.

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

  1. Virtual and $15$cm from the mirror

  2. Real and $20$cm from the mirror

  3. Virtual and $20$cm from the mirror

  4. Real and $10$cm from the mirror

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Correct Option: B
Explanation:

Image of an object placed at center of curvature is inverted, real and of the same size and is formed at the center of curvature. Hence image will be real and at the center of curvature (20 cm from mirror).

Formula of focal length in convex lens is

physics reflection of light in spherical mirrors focus and focal length spherical mirror formula and magnification reflection of light by curved surfaces

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

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

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

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

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Correct Option: B