Notes
Charge and circuits
- Like charges repel, opposite charges attract. Electrons move; protons stay put. Conductors let charge flow; insulators do not.
- Current (amperes) is the flow of charge, voltage (volts) is the push, and resistance (ohms) opposes current.
Ohm's law and power
- $V = IR$, $\displaystyle I = \frac{V}{R}$, $\displaystyle R = \frac{V}{I}$. Electric power $P = IV$.
- Series: one path, resistances add, same current. Parallel: branches share the same voltage and work independently.
Magnetism
- Like poles repel, opposite poles attract; a cut magnet still has two poles. Current creates a magnetic field, so a coil with an iron core is an electromagnet.
- Motors change electrical energy to mechanical energy. Generators change mechanical energy to electrical energy by electromagnetic induction.
Topics in this unit
Each topic has its own short notes and practice.
Practice
$\displaystyle I = \frac{V}{R} = \frac{24}{6} = 4$ A.
$\displaystyle R = \frac{V}{I} = \frac{10}{0.5} = 20$.
$P = IV = 120 \times 5 = 600$ W.
$10 + 15 = 25$.
Losing electrons leaves the rod positive.
Generators use induction to produce current.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A 12 V battery is connected to a circuit with two resistors in series: 2 $\Omega$ and 4 $\Omega$.
(a) Find the total resistance of the circuit.
Show the answer and scoring guide
$R = 2 + 4 = 6\ \Omega$.
Check off the points you earned:
(b) Find the current in the circuit.
Show the answer and scoring guide
$\displaystyle I = \frac{V}{R} = \frac{12}{6} = 2$ A.
Check off the points you earned:
(c) Calculate the power supplied by the battery and state what happens to the current if one resistor is removed from the circuit (leaving a closed loop).
Show the answer and scoring guide
$P = IV = 2 \times 12 = 24$ W. With one resistor removed, total resistance drops, so the current increases (for example $\displaystyle \frac{12}{2} = 6$ A).
Check off the points you earned: