Explanation

A typical diffraction grating can have 400 to 50,000 lines per centimeter, depending on precision and application.

Higher line densities provide better spectral resolution for analyzing light.

Explanation

The fine ruling (track spacing) on a CD is about 0.5 micrometers (µm).

This microscopic spacing allows the CD to store large amounts of data through optical encoding.

Explanation

Sound waves are mechanical vibrations that can disturb air particles around a candle flame.

This disturbance causes the flame to flicker due to pressure variations in the air.

Explanation

Explanation

Apparent weight = Normal force, and when moving upward with acceleration g, total acceleration = g + g = 2g.

So, Apparent weight = m × (g + g) = 2mg.

Explanation

When moving with constant velocity, there is no net acceleration acting on the body.

Therefore, the apparent weight remains the same as actual weight — not changed.

Explanation

Kinetic Energy (K.E) = ½ × mass × velocity² = ½ × 2 × (4)² = 1 × 16 = 16J

The formula directly gives 16 joules for the given mass and velocity.

Explanation

 The meeting was held in the conference room.

یہ ملاقات کانفرنس روم میں ہوئی۔

Use “in” when something happens inside an enclosed space, like a room, hall, or building.

Explanation

My sister has been living in Paris for three years.

میری بہن تین سال سے پیرس میں رہ رہی ہے۔

We use "for" with a duration of time (e.g., for two hours, for ten years).

Explanation

We use “on” with days and dates (e.g., on Monday, on Friday, on July 5).
This sentence refers to a specific day, so:  “On Friday” is correct.