How can a moving coil galvanometer be converted into (a) an ammeter of range 0 to I and (b) a voltmeter of range 0 to V? Derive the resistance needed in each case, with circuit diagrams.

1. 1 · Explain the need. A galvanometer reads only up to a small current I_g and has its own resistance G.
2. 2 · Draw both circuits. [Ammeter: G with shunt S in parallel, current I splitting into I_g and I − I_g. Voltmeter: G with R in series, V across both]
3. 3 · Ammeter. I_g G = (I − I_g)S, so S = I_g G/(I − I_g); low resistance, joined in series in the circuit.
4. 4 · Voltmeter. V = I_g(G + R), so R = V/I_g − G; high resistance, joined in parallel across the points.
5. 5 · Ideal values. Ideal ammeter: zero resistance. Ideal voltmeter: infinite resistance.
6. 6 · Real life. An analogue multimeter switches shunts and series resistors with its dial.
7. 7 · Close in one line. So, a low shunt in parallel makes an ammeter, and a high series resistance makes a voltmeter.

Scoring tip: Draw both circuits and mark the current through each branch. The same potential difference across G and S is the key line for the shunt.