Tag: technical terms related to lens

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Questions Related to technical terms related to lens

Multiple choice physics lens technical terms related to lens terms related to lenses introduction to lenses and its types

Which of the following term is not associated with a lens ?

  1. Aperture

  2. Focal length

  3. Principal focus

  4. Efficiency
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aperture of a lens is the length of the surface of lens exposed for incident light.Focal length is the distance between focus of the lens and lens optical center.Principal focus is the focus from which a ray of light traveling parallel to optical axis passes through or appears to pass through after refraction.There is no term like efficiency of a lens.but there is magnification of a lens.

Multiple choice physics lens technical terms related to lens terms related to lenses introduction to lenses and its types

The value of the focal length of the lens is equal to the value of the image distance when the rays are

  1. Passing through the optic centre

  2. Parallel to the principal axis

  3. Passing throught he focus

  4. Over the mirror
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the object is placed at infinity, i.e., when the rays are parallel to the principal axis, the value of focal length is equal to the value of the image distance.

i.e., object distance , $u=\infty$
From lens formula,

$\dfrac 1f=\dfrac 1u+\dfrac 1v\\\implies \dfrac 1f=\dfrac 1\infty+\dfrac 1v\\\implies f=v$
i.e., image distance is equal to focal length of the lens.

Multiple choice physics lens technical terms related to lens terms related to lenses introduction to lenses and its types

A thin plano-convex lens acts like concave mirror of focal length $0.2m$ when silvered at its plane surface. Refractive index of the material of lens is $1.5$. Radius of curvature of convex surface of the lens is

  1. $0.1m$

  2. $0.2m$

  3. $0.4m$

  4. $0.8m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a silvered plano-convex lens, the focal length is given by 1/f = 2/f_lens + 1/f_mirror. With f_mirror = infinity (plane surface) and f_lens = R/(n-1), the effective focal length is R/(2(n-1)). Setting this to 0.2m with n=1.5 yields R = 0.2m.