IGCSE Physics Paper-1: Specimen Questions with Answers 136 - 138 of 149

What is the melting point of pure water?

Answer

b.

Explanation

• The temperature at which the substance or solid will get is known as melting point.
• The melting point of pure water is
• And at the temperature the liquid gets evaporate is known as boiling point.
• The boiling point of pure water is

Sodium-24 has half-life of 15 hours. If there are 1600g of Na-24 initially, how will it take for 1400g of Na-24 to decay?

Answer

a.

Explanation

For finding half-life the formula is

In () =-kt

Here,

K =

K = constant and = half life

K =

In () =-kt

In ()

In

t =

t = 45 hrs

(OR)

3 half-lives for sample to decay from 1600g to 200g

i.e..

45hours for 1400g of sodium-24 to decay

The circuit shown contains three lamps and 4 switches

Which switches must be closed to light up lamp 1 and lamp 3?

Answer

c.

Explanation

• The given circuit is a parallel circuit. In a parallel circuit the current passes in a closed path.
• If there is any breakage the current does not flows through it.
• From the circuit, the switch 1, switch 2 and switch 5 must be closed to light the lamp 3.