PPSC MCQs

Non-luminous objects become visible when illuminated.
Reflected light enters the eyes and forms an image.

Sound waves can reflect from distant surfaces.
If the delay is sufficient, the reflected sound is heard as an echo.

Reflection from a smooth surface obeys equal incidence and reflection angles.
Both angles are measured from the normal.

Soft porous materials absorb part of the sound energy.
This reduces excessive reverberation and improves clarity.

A plane mirror forms a virtual image behind the mirror.
The image is upright, same-sized, and left-right reversed.

Bats emit high-frequency sound pulses and detect returning echoes.
This helps them navigate and locate prey.

Light changes speed when moving between media.
This speed change usually causes bending, called refraction.

Light from the submerged part changes direction when leaving water.
The brain traces rays backward and sees an apparent displacement.

Spectacle lenses change the convergence of light entering the eye.
They help focus images correctly on the retina.

The iris changes the size of the pupil.
This regulates how much light enters the eye.

The lens focuses incoming light onto the retina.
Photoreceptor cells then convert light into nerve signals.

Red light has the longest wavelength in the visible spectrum.
Violet has the shortest visible wavelength.