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A platinum-resistance thermometer has a resistance of 5&O...

A platinum-resistance thermometer has a resistance of 5Ω at 0°C and 9Ω at l00°C. Assuming that resistance changes uniformly with temperature, calculate the resistance of the thermometer when the temperature is 45°C.

A.

13.9 Ω

B.

8.9 Ω

C.

6.8 Ω

D.

3.2 Ω

E.

1.8 Ω

Correct answer is C

θ100=RθR0R100R0

45100=Rθ595

45×4=100(Rθ5)

180=100Rθ500

180+500=100Rθ

Rθ=680100

Rθ=6.8Ω