How to calculate Drift Velocity: Step-by-step examples

📚 Quick Study Guide

🔍 Drift velocity ($v_d$) is the average velocity attained by charged particles (e.g., electrons) in a material due to an electric field. 💡 The formula for drift velocity is: $v_d = \frac{I}{n A q}$, where:
• $I$ is the current.
• $n$ is the charge carrier density (number of charge carriers per unit volume).
• $A$ is the cross-sectional area of the conductor.
• $q$ is the charge of a single charge carrier (e.g., the elementary charge, $1.602 × 10^{-19}$ Coulombs for electrons).
📝 Current ($I$) is related to drift velocity by: $I = n A q v_d$. ⚗️ The units for drift velocity are typically meters per second (m/s). ⚡ Higher current or lower charge carrier density leads to a higher drift velocity, given constant area and charge.

Practice Quiz

1. What is drift velocity?
   1. The velocity of an electron in a vacuum.
   2. The average velocity of charged particles due to an electric field.
   3. The maximum velocity of a proton in a nucleus.
   4. The speed of light in a medium.
2. What is the formula for drift velocity ($v_d$)?
   1. $v_d = nAq/I$
   2. $v_d = I/(nAq)$
   3. $v_d = nAqI$
   4. $v_d = (nAq)^2/I$
3. What does 'n' represent in the drift velocity formula?
   1. The number of electrons in the circuit.
   2. The charge carrier density.
   3. The total voltage.
   4. The resistance of the wire.
4. If the current in a wire increases, what happens to the drift velocity (assuming other factors remain constant)?
   1. It decreases.
   2. It increases.
   3. It stays the same.
   4. It becomes zero.
5. A copper wire has a cross-sectional area of $2.0 \times 10^{-6} m^2$ and carries a current of 10 A. If the charge carrier density is $8.5 \times 10^{28} m^{-3}$, what is the drift velocity?
   1. $3.68 \times 10^{-4} m/s$
   2. $3.68 \times 10^{-3} m/s$
   3. $3.68 \times 10^{-5} m/s$
   4. $3.68 \times 10^{-6} m/s$
6. What is the unit for drift velocity?
   1. Amperes (A)
   2. Volts (V)
   3. Meters per second (m/s)
   4. Ohms (Ω)
7. If the charge carrier density decreases, what happens to the drift velocity (assuming other factors remain constant)?
   1. It decreases.
   2. It increases.
   3. It stays the same.
   4. It fluctuates randomly.