Question

In a step up transformer, which one of the following statements is correct?

• A. Number of turns in the secondary coil is less than in primary coil.
• B. Voltage in secondary coil is less than voltage in primary coil.
• C. Current in the primary coil is more than current in the secondary coil.
• D. Current in the primary coil is equal to current in the secondary coil.

Hint:

Remember that a transformer cannot create power out of nothing! If a transformer steps up the voltage, it must step down the current proportionally to keep the total power product ($V \times I$) perfectly balanced on both sides.

Answer 1

The Correct Option is C

Step 1: What is asked.
We must pick the true statement about a step-up transformer. A step-up transformer raises the voltage from the primary side to the secondary side.
Step 2: The transformer relation.
For an ideal transformer, \[ \frac{V_s}{V_p} = \frac{N_s}{N_p} = \frac{I_p}{I_s} \] where $p$ is primary and $s$ is secondary.
Step 3: What step-up means.
Step-up means $V_s > V_p$. So the secondary has more turns, $N_s > N_p$. This already rules out the option saying the secondary has fewer turns and the one saying the secondary voltage is lower.
Step 4: Energy is conserved.
An ideal transformer does not create power, so input power equals output power: \[ V_p I_p = V_s I_s \]
Step 5: Compare the currents.
Rearrange: \[ \frac{I_p}{I_s} = \frac{V_s}{V_p} > 1 \;\Rightarrow\; I_p > I_s \] So the primary current is larger than the secondary current. Higher voltage out means lower current out.
Step 6: State the answer.
The correct statement is that the current in the primary coil is more than in the secondary coil, which is option (3). \[ \boxed{I_p > I_s} \]