A moving-coil galvanometer is a device for detecting and measuring electric current - Leaving Cert Physics - Question b - 2022

The diagram should depict the following components:

• A coil
• A magnet
• A soft iron core
• A scale
• A pointer Make sure each component is clearly labelled as per the requirements.

The moving-coil galvanometer operates on the principle of electromagnetic induction. When an electric current passes through the coil situated in a magnetic field, it experiences a force due to magnetic interaction. The resulting torque causes the coil to rotate, which in turn moves the pointer across the scale. The extent of deflection of the pointer is proportional to the magnitude of the current passing through the coil.

To convert a galvanometer into an ammeter, a low-resistance shunt resistor is connected in parallel with the galvanometer. This allows most of the current to pass through the shunt, while a small, measurable portion passes through the galvanometer.

To convert a galvanometer into an ohmmeter, a variable resistor is connected in series with the galvanometer and a power supply. This setup allows the galvanometer to measure the resistance by detecting the current flowing through the unknown resistor.

Using the formula for voltage in terms of resistance and current:

$V = I imes R$ Substituting the known values: $10 = 0.05 imes (R + 0.7)$ Solving for R gives: R = rac{10}{0.05} - 0.7 = 199.3 \ ext{Ω} Thus, the resistance of the multiplier is approximately 199.3 Ω.