Concepts addressed: velocity in an electric field, electrical power, and analytical skills.
Grade level: 11th
Scenario:
When a light switch is off, the electric circuit inside the wall of your house is interrupted, so neither an electric field nor electrons can flow through it. The moment you flip the switch on you close the circuit, meaning that electrons (and the electric field) are free to flow through the circuit again, and reach whatever device you wanted to power.
Assuming the wiring in your house is full copper 12AWG, and that the length of the cable connecting the switch to the overhead light bulb (60W LED) is 3m.
- How long would it take an electron in the switch to reach the light bulb?
- Is the result surprising? Why?
- Can you explain it? How long would it take light to travel the same distance?
Data:
Diameter of 12 AWG wire: 2.053mm
Voltage of household’s electric system: 220V (EU) || 120V (US)
Density of Carriers in copper: 8.5 1028 carriers/m³
Speed of light: 299 792 458 m/s
Useful calculators:
- Circumference calculator – https://www.omnicalculator.com/math/circumference
- Wire Resistance calculator – https://www.omnicalculator.com/physics/wire-resistance
- Ohm’s Law calculator – https://www.omnicalculator.com/physics/ohms-law
- Drift Velocity calculator – https://www.omnicalculator.com/physics/drift-velocity
- Velocity calculator – https://www.omnicalculator.com/physics/velocity
Question 1 hints:
Question 2 hints:
Question 3 hints:
Solutions :
Step-by-Step solutions :
- Is the difficulty level right for your class?
- How would you use it in class?
- How would you improve this scenario?
- A bonus: what are you teaching next week? We'd love to prepare a scenario for you
