# IGCSE Physics Paper-1: Specimen Questions with Answers 135 - 138 of 149

## Question 135

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### Question

MCQ▾

The diagram shows a wave.

How many wavelengths are there between X and Y?

Choice (4)
a.
b.
c.
d.1

a.

### Explanation

Total wavelengths =+ 1+

=

=

=

## Question 136

Edit

### Question

MCQ▾

What is the melting point of pure water?

Choice (4)
a.
b.
c.
d.

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

## Question 137

Edit

### Question

MCQ▾

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?

Choice (4)
a.45 hrs
b.50 hrs
c.1 day
d.40 hrs

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

## Question 138

Edit

### Question

MCQ▾

The circuit shown contains three lamps and 4 switches

Which switches must be closed to light up lamp1 and lamp3?

### Choices

Choice (4)
a.switch 1,2, 3 and 4 only
b.switch5 only
c.switch1, switch2 and switch5 only
d.switch1 and switch2 only