Question

Fig. 12.1 shows a refrigerator.

(a) (i) The refrigerator uses electrical energy to:
• power the electric motor which operates the cooler
• light the lamp inside the refrigerator.

The electric motor and the lamp are connected in parallel.
The circuit symbol for a motor is M
Complete the circuit diagram for the refrigerator shown in Fig. 12.2.

                    Fig. 12.2

(ii) State the name of component X.

……………………………………………………………………………………………………………………. 

(iii) State the purpose of component X in this circuit.

…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….

(b) Food is kept in a refrigerator so that it stays fresh for longer.
Another way to preserve food is to treat it with γ-radiation.
γ-radiation is a form of ionising radiation.
State the name of one other form of ionising radiation.
……………………………………………………………………………………………………………………..
(c) The volume of air in the refrigerator is 0.25m$^{-3}$.
The density of the air is 1.28kg/m$^{-3}$.
Calculate the mass of the air in the refrigerator in grams.

                                           mass = ……………………………………………….g

(d) Fig. 12.3 shows a liquid-in-glass thermometer.

The thermometer is used to measure the temperature inside the freezing compartment of the refrigerator. This temperature is –18°C.
Table 12.1 gives some information about four liquids.

(i) Identify all the liquids from Table 12.1 that are suitable for use in this thermometer.
……………………………………………………………………………………………………………………. 
(ii) State the physical property of the liquid in the thermometer that varies with temperature.
……………………………………………………………………………………………………………………. 

▶️Answer/Explanation

Ans:   12(a)(i) correct symbol for lamp ;
lamp and motor in parallel ;

12(a)(ii) fuse ; 
12(a)(iii) protect circuit ; 
12(b) alpha / beta / X-rays ; 
12(c) mass = density × volume (in any form) / 1.28 × 0.25 ;
evidence of conversion of mass to grams ;
= 320 (g) ;

12(d)(i) ethanol, mercury and methanol ; 
12(d)(ii) density / volume ;