*Question T5C08:
What is the formula used to calculate electrical power (P) in a DC circuit?*  

*Correct Answer is  A: P = I × E*  

### AI Response: (may contain errors)  

To calculate electrical power (P) in a DC circuit, the correct formula is:

$$P = I \times E$$

where:
- $P$ = power in watts (W)
- $I$ = current in amperes (A)
- $E$ = voltage in volts (V)

### Explanation of the Correct Answer:
- The formula $P = I \times E$ is derived from Ohm's Law, which states that voltage ($E$) is equal to current ($I$) multiplied by resistance ($R$). In a DC circuit, power is the product of current and voltage, making this formula essential for calculating power.

### Why the Other Choices are Incorrect:
- **Choice A: P = I × E**  
  - This is the correct answer.

- **Choice B: P = E / I**  
  - This formula rearranges Ohm's Law to find current ($I$) when power and voltage are known. It is not the correct formula for calculating power directly.

- **Choice C: P = E – I**  
  - This formula does not represent any standard electrical relationship. Power cannot be calculated by simply subtracting current from voltage.

- **Choice D: P = I + E**  
  - Similar to choice C, this formula does not represent a valid relationship in electrical circuits. Power is not the sum of current and voltage.

### Useful Formulas and Rules of Thumb:
- **Ohm's Law**:  
  $$E = I \times R$$  
  This relates voltage, current, and resistance.

- **Power in terms of resistance**:  
  $$P = \frac{E^2}{R}$$  
  This can be used if voltage and resistance are known.

- **Power in terms of current**:  
  $$P = I^2 \times R$$  
  This can be used if current and resistance are known.

Understanding these relationships will help you solve various problems related to electrical power in DC circuits.