Applied Electricity and Circuit Theory Don't do this

3 Mistakes That Cost Marks in Circuit Basics

Can you name 3 mistakes that cost marks in circuit basics?

Lesson notes

Define charge, current, voltage and power and calculate P = VI and energy for a DC load

Key points

Current gets used up: Charge is conserved, so current in equals current out; the load converts energy, not charge.
Energy in watts: Power is a rate in watts; energy is power times time, in joules or kilowatt-hours.
Ignoring sign convention: With current entering the plus terminal, positive VI means absorbed power; flip it and you lose marks.

Takeaway: Charge is conserved; energy is transferred, and W = Pt.

Quick check: A 12 V lamp draws 2 A. What happens to the current leaving it?

It equals the current in
It drops to nearly zero
It is used up as light

Charge is conserved; the lamp transfers energy, so current out equals current in.

currentvoltagepowerpassive sign convention

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