Question

In step-up transformer, the value of current in secondary coil compared to primary coil is

• A. equal
• B. less
• C. more
• D. none of these

Hint:

Think of a transformer as trading voltage for current to conserve power. \textbf{Step-UP} transformer: Voltage goes UP, so current must go DOWN. \textbf{Step-DOWN} transformer: Voltage goes DOWN, so current must go UP.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A transformer is a device that transfers electrical energy from one circuit to another through electromagnetic induction. A step-up transformer increases the AC voltage from the primary coil to the secondary coil.
Step 2: Key Formula or Approach:
For an ideal transformer (assuming 100% efficiency and no energy loss), the power input to the primary coil is equal to the power output from the secondary coil.
Power \(P = V \times I\), where \(V\) is voltage and \(I\) is current.
Therefore, for an ideal transformer:
\[ P_{\text{primary}} = P_{\text{secondary}} \] \[ V_p I_p = V_s I_s \] where \(p\) denotes the primary coil and \(s\) denotes the secondary coil.
Step 3: Detailed Explanation:
In a step-up transformer, the secondary voltage is greater than the primary voltage:
\[ V_s>V_p \] Using the power conservation equation \(V_p I_p = V_s I_s\), we can write the ratio of the currents as:
\[ \frac{I_s}{I_p} = \frac{V_p}{V_s} \] Since \(V_s>V_p\), the ratio \(\frac{V_p}{V_s}\) is less than 1.
\[ \frac{I_s}{I_p}<1 \] This implies that \(I_s<I_p\).
So, in a step-up transformer, while the voltage is increased, the current is decreased proportionally.
Step 4: Final Answer:
The value of the current in the secondary coil of a step-up transformer is less than the current in the primary coil. Option (B) is correct.