# Electricity & Magnetism — ACT Science
Electricity and magnetism concepts appear in ACT Science passages about circuits, electromagnetic experiments, and energy consumption. You need to understand basic relationships between voltage, current, and resistance.
Key Concepts
Electric Current and Circuits
- Current (): flow of electric charge (amperes).
- Voltage (): "push" that drives current (volts).
- Resistance (): opposition to current flow (ohms).
- Ohm's Law: .
Series vs. Parallel Circuits
- Series: one path. More resistors → less current. If one breaks, all stop.
- Parallel: multiple paths. Each path gets full voltage. Total current increases.
Power
- (watts).
- Higher power → more energy consumed per second.
Magnetism Basics
- Magnets have north and south poles.
- Like poles repel; unlike poles attract.
- Electric current creates a magnetic field.
- Changing magnetic fields create electric current (electromagnetic induction).
Static Electricity
- Objects can become charged by friction.
- Like charges repel; opposite charges attract.
Worked Example
Passage summary: Students vary the resistance in a circuit and measure the current with a 12 V battery.
| Resistance (Ω) | Current (A) |
|---|---|
| 2 | 6.0 |
| 4 | 3.0 |
| 6 | 2.0 |
| 12 | 1.0 |
Q: What relationship does this data show?
A: Current is inversely proportional to resistance (at constant voltage), consistent with Ohm's law: .
Practice Questions
1. If voltage doubles and resistance stays the same, what happens to current?
Current doubles ().
2. In a series circuit with a 12 V battery and two 6 Ω resistors, what is the current?
. .
3. A compass needle deflects when placed near a wire carrying current. What does this demonstrate?
Electric current produces a magnetic field.
Want to check your answers and get step-by-step solutions?
Summary
- Ohm's law: . More resistance → less current (at constant voltage).
- Series circuits: one path, resistances add.
- Parallel circuits: multiple paths, each gets full voltage.
- Current creates magnetic fields; changing magnetic fields create current.