# Physics - electricity

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A thermo junction of iron and copper connected to a galvanometer cannot be used to measure temp above about 450K, whereas one of iron-constantan may be used to at least 875K. What is the explanation?

Is it possible that melting at the junction point is a limiting factor?

• Physics - electricity -

Trying to find the charge on a balloon that has a radius of 10cm. It attracts circle of paper, r=3mm with a thickness of .1mm. They come together when the balloon got with 10cm.

It attracts circles of tin foil when the balloon got within 20 cm. Tin foil circles, r=1mm and thickness=.01mm.
Thanks

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