Tag: spherical mirror formula and magnification

Questions Related to spherical mirror formula and magnification

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

An object is placed at a distance of $50\ cm$ from a convex mirror. A plane mirror is placed in front of the convex mirror in such a way that it covers half of the convex mirror. If the distance between object and plane mirror is $30\ cm$ then there is no parallax between the images formed by two mirrors, the radius of curvature of convex mirror 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. $50\ cm$

  2. $25\ cm$

  3. $12.5\ cm$

  4. $100\ cm$

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Correct Option: A