Current (Grade 10 NSC Matric Physical Sciences): Revision Notes

Worked Example 1: Basic Current Calculation

Question: An amount of charge equal to 45 C moves past a point in a circuit in 1 second. What is the current in the circuit?

Solution:

• Step 1: Identify what we know

  • Charge (Q) = 45 C
  • Time (Δt) = 1 s
  • Need to find: Current (I)

• Step 2: Apply the formula

  • $I = \frac{Q}{\Delta t}$
  • $I = \frac{45 \text{ C}}{1 \text{ s}}$
  • I = 45 A

• Step 3: State the answer

  • The current is 45 A

Worked Example 2: Current with Different Time

Question: An amount of charge equal to 53 C moves past a fixed point in a circuit in 2 seconds. What is the current in the circuit?

Solution:

• Step 1: Identify what we know

  • Charge (Q) = 53 C
  • Time (Δt) = 2 s
  • Need to find: Current (I)

• Step 2: Apply the formula

  • $I = \frac{Q}{\Delta t}$
  • $I = \frac{53 \text{ C}}{2 \text{ s}}$
  • I = 26.5 A

• Step 3: State the answer

  • The current is 26.5 A

Worked Example 3: Current from Electron Flow

Question: 95 electrons move past a fixed point in a circuit in one tenth of a second. What is the current in the circuit?

Solution:

• Step 1: Identify what we know

  • Number of electrons = 95
  • Time (Δt) = 0.1 s
  • Charge of one electron = $1.6 \times 10^{-19}$ C

• Step 2: Calculate total charge

  • $Q = 95 \times 1.6 \times 10^{-19} \text{ C}$
  • $Q = 1.52 \times 10^{-17} \text{ C}$

• Step 3: Apply the current formula

  • $I = \frac{Q}{\Delta t}$
  • $I = \frac{1.52 \times 10^{-17} \text{ C}}{0.1 \text{ s}}$
  • $I = 1.52 \times 10^{-16} \text{ A}$

• Step 4: State the answer

  • The current is 1.52 × 10⁻¹⁶ A