IB DP Physics: HL复习笔记11.2.4 Transformer Calculations

Transformer Calculations

  • The transformer equation is:
  • Where:
    • Ns = number of turns in the secondary coil
    • Np = number of turns in the primary coil
    • εs = output voltage from the secondary coil (V)
    • εp = input voltage in the primary coil (V)

There are two types of transformers:

  • Step-up transformer (increases the voltage of the power source) where Ns > Np
  • Step-down transformer (decreases the voltage of the power source) where Np > Ns
  • For an ideal transformer, there is no electrical energy lost and it is 100% efficient
  • This means the power in the primary coil equals the power in the second coil;
  • Where:
    • Ip = current in the primary coil (A)
    • Is = output current from the secondary coil (A)

Worked Example

A step-down transformer turns a primary voltage of 0.5 kV into a secondary voltage of 100 V. Calculate the number of turns needed in the secondary coil if the primary coil contains 3000 turns of wire.

Step 1: List the known quantities

    • Primary voltage, εp = 0.5 kV = 0.5 × 103 V
    • Secondary voltage, εs = 100 V
    • Number of turns in the primary coil, Np = 3000 turns

Step 2: Write down the transformer equation