Fig. 3.1 shows a laboratory freezer. [Figure 3.1] The door is closed and the freezer is switched on. A cold liquid is pumped through the copper pipe at the top of the freezer. The temperature of the air next to the copper pipe decreases quickly.

1. (a)Explain how the temperature of the rest of the air in the freezer decreases.[3]
2. (b)(i)The thick insulation shown in Fig. 3.1 is made from a plastic material. The plastic material in the insulation is a poor thermal conductor. Describe how thermal energy is transferred through a plastic material.[2]
3. (b)(ii)The plastic material also contains a large number of small air bubbles. Explain how the air bubbles reduce the transfer of thermal energy through the insulation.[3]

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