A meter maker in code

You will write four small functions that a maker of meters would need.

The idea. In a radial field, $NIAB = k\phi$. A shunt makes an ammeter, $S = \dfrac{I_gG}{I - I_g}$. A series resistor makes a voltmeter, $R = \dfrac{V}{I_g} - G$. An ammeter in a circuit adds its own resistance. Use SI units: m², T, A, V and ohm.

Your tasks.

1. In deflection, return the deflection $\phi$ in radian for a coil of N turns, area A, radial field B, spring constant k and current I.
2. In shunt, return the shunt in ohm for a coil of resistance G and full-scale current Ig, for an ammeter that reads up to I.
3. In series_resistor, return the resistor in ohm that makes a voltmeter that reads up to V.
4. In ammeter_reading, return the current in A that an ammeter of resistance RA reads when it is in series with a resistor R and a cell of emf emf. The cell has no internal resistance.