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(a) An ammeter with resistance \( R_{A} \) is connected in series with a resistor \( R \) and a battery of \( \operatorname{emf} \varepsilon \) and internal resistance \( r \).
\( \mathrm{P} \) The current measured by the ammeter is \( I_{A} \). Find the current

W 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 \( R \). The more "ideal" the ammeter, the smaller the difference between this current and the current \( I_{A} \). (b) If \( R=3.80 \Omega, \xi=7.50 \mathrm{~V} \) and \( r=0.45 \Omega \), 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.
(c) Explain why your answer in part (b) represents a maximum value.
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