$CATEGORY: Science - Khan Academy/10.Light-Reflection and Refraction/10.Light-Reflection and Refraction--Refraction Of Light

//Multiple Choice

What is the power of a lens?
{
= The ability of a lens to converge or diverge light rays
~ The thickness of a lens
~ The focal length of a lens
~ None of the Above
}

Which of the following is the correct formula for the power of a lens?
{
~ P \= 1 / 2f
= P \= 1 / f
~ P \= 2f
~ None of the Above
}

What is the SI unit of the power of a lens?
{
~ Meter (m)
= Dioptre (D)
~ Centimeter (cm)
~ None of the Above
}

What is the power of a lens with a focal length of 2 meters?
{
= 0.5 D
~ 2 D
~ 0.2 D
~ None of the Above
}

If two lenses of power P1 and P2 are placed in contact, the total power is given by
{
~ P \= P1 × P2
~ P \= P1 − P2
= P \= P1 + P2
~ None of the Above
}

A convex lens has a focal length of 50 cm. What is its power?
{
= 2 D
~ 5 D
~ 1 D
~ None of the Above
}

What is the power of a concave lens with a focal length of 100 cm?
{
~ +1 D
= -1 D
~ +2 D
~ None of the Above
}

Which combination of lenses will give zero power?
{
= A convex lens and a concave lens of the same focal length
~ Two convex lenses
~ Two concave lenses
~ None of the Above
}

What happens to the power of a lens if its focal length decreases?
{
= Power increases
~ Power decreases
~ Power remains the same
~ None of the Above
}

//True or False

The power of a lens is directly proportional to its focal length. {F}

The unit of power of a lens is the dioptre (D). {T}

A concave lens has a positive power. {F}

If two lenses are placed in contact, the total power is the sum of the powers of individual lenses. {T}

A lens with a shorter focal length has a higher power. {T}

The power of a convex lens is negative. {F}

Power of a lens is the ability to bend light rays and is measured in dioptres. {T}

A lens with a focal length of 1 meter has a power of 10 dioptres. {F}

If the focal length of a lens is increased, its power decreases. {T}

Two lenses with equal but opposite powers placed together will have a total power of zero. {T}


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