Problem

1. (a) An ammeter with resistance

R_A

is connected in series with a resistor

R

, a battery of emf

\epsilon

and internal resistance

r

. The current measured by the ammeter is

I_A

. Find the current through the circuit if the ammeter is removed so that the battery and the resistor form a complete circuit. Express your answer in terms of

I_A

r

R_A

and

R

. Show that more "ideal" the ammeter, the smaller the difference between this current and the current

I_A

. 2. (b) If

R = 3.80 \tau

\epsilon = 7.50 \text{ V}

and

r = 0.45 \tau

, find the maximum value of the ammeter resistance

R_A

so that

I_A

is within

99\%

of the current in the circuit when the ammeter is absent. 3. (c) Explain why your answer in part (b) represents a maximum value.

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