Physics unofficial markscheme p4 5 6

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P4

1)alpha is not penetrating so can't be used for tracers only gamma rays used [1] [Could you also say that, on account of the fact that alpha radiation is so ionizing, it is unsafe to use as a tracer?]

2)half life of radioactive substance or how much it decays shows how long it will be active [1]
3)head is focused so only gamma rays hit the tumour to concentrate it. This reduces the exposure to healthy living tissue[2]

4)the thing that was rubbed become positively charged as it loses electrons

5)antistatic sprays reduce build up of electons so stop the transfer of charge from one insulator to another
6)the risk of the petrol handle is explosions or ignition/sparking the fuel. It is useful as it has insulating handle stops electric shock??It earths it as no build up[3] [This was only two marks. It asked you to describe one risk and one benefit.]
7)output voltage was output current *output resistance
8)the new iron more useful as it has a variable resistor so the current flow can be changed by changing resistance