Transformer Equations Flashcards

All 6 cards in this deck

What is the transformer equation linking potential differences and numbers of turns?

$\dfrac{V_p}{V_s} = \dfrac{n_p}{n_s}$

What equation links the currents and potential differences of a 100% efficient transformer?

$V_s \times I_s = V_p \times I_p$ (power output = power input).

What are the steps to find the number of turns on the secondary coil of a transformer?

e.g. $V_p = 1.5\ \text{V}$, $V_s = 5.0\ \text{V}$, $n_p = 150$

1. Write the equation: $\dfrac{V_p}{V_s} = \dfrac{n_p}{n_s}$, so $\dfrac{1.5}{5.0} = \dfrac{150}{n_s}$.
2. Rearrange: $n_s = \dfrac{150}{0.3}$.
3. $n_s = 500$ turns.

What are the steps to find the current drawn from the input supply for a given power output?

e.g. output power $60\ \text{W}$, input p.d. $230\ \text{V}$, 100% efficient

1. Power input = power output: $V_p I_p = 60\ \text{W}$.
2. Rearrange: $I_p = \dfrac{60}{230}$.
3. $I_p = 0.26\ \text{A}$.

In a 100% efficient transformer, what does $V_s \times I_s$ give?

The power output at the secondary coil, in watts.

True or false? In a step-up transformer the current in the secondary coil is larger than in the primary coil.

False. If the pd is stepped up, the current is stepped down, because the power output equals the power input.