Which of these could be the output for a dynamo? A - Edexcel - GCSE Physics - Question 9 - 2018 - Paper 1

To find the potential difference ($V_s$) across the secondary coil, we can use the transformer equation:

$\frac{V_s}{V_p} = \frac{N_s}{N_p}$

Where:

• $V_p = 25\, V$ (potential difference across the primary coil)
• $N_p = 30$ (number of turns on the primary coil)
• $N_s = 150$ (number of turns on the secondary coil)

Substituting the known values:

$\frac{V_s}{25} = \frac{150}{30}$

This simplifies to:

$\frac{V_s}{25} = 5$

Rearranging gives:

$V_s = 25 \times 5 = 125\, V$

High voltage transmission cables are implemented to reduce energy loss due to resistance in the wires. By increasing voltage, the current can be decreased for the same power level, since

$P = V \times I$

This means less energy is lost as heat, per the relationship $P = I^2 \times R$, where $R$ is the resistance of the wires. Additionally, transformers are used to step up the voltage for transmission and step it down for safe consumption. This combination allows power to be distributed more effectively over long distances with minimal losses.