Answer to Question 4

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A solenoid of length 2.5 cm has 200 turns.  A current of 1.65 A flows through it.  Calculate the resulting magnetic field strength.   Give your answer to an appropriate number of significant figures.

The number of turns per metre = 200 turns 0.025 = 8000 turns per metre.

B = 4p 10-7 H m-1 8000 m-1 1.65 A = 0.0166 T = 0.017 T (= 17 mT)

2 significant figures as the length is to 2 s.f.