A basic property of matter that causes electric forces; can be positive or negative. Moving charge creates electric current.

The invisible region around a charged object where other charges feel a force. Explains attraction and repulsion at a distance.

The rate of flow of electric charge, measured in amperes (A). In metals, it is mainly moving electrons.

Electric potential difference; the "push" that drives current through a circuit, measured in volts (V).

How much a material or component opposes current, measured in ohms (Ω). Higher resistance means less current for the same voltage.

A safety device with a thin wire that melts and breaks the circuit if the current is too high.

Electric potential difference between two points; the "push" that drives current, measured in volts (V).

An equation that relates voltage (V), current (I), and resistance (R): V = I × R.

Electricity and Simple Circuits — SHS Science Foundations: Integrated Chemistry, Biology, and Physics

Q: A circuit uses a 12 V battery and a 4 Ω resistor. What is the current in the circuit, and what happens to the current if you replace the resistor with an 8 Ω one (battery unchanged)?

Current is 2 A; with 8 Ω, current becomes 1 A. Use Ohm's law: I = V / R. With 4 Ω: I = 12 / 4 = 3 A (this makes A and B wrong). With 8 Ω: I = 12 / 8 = 1.5 A (this makes D wrong). So the correct pair is 2 A and 1 A? Wait, recalculate: 12 / 4 = 3 A and 12 / 8 = 1.5 A, so option B is correct.

Electric Charge and Electric Current

What Is Electric Charge?

Electricity begins with electric charge. Protons carry positive charge and electrons carry negative charge. Charged objects can attract or repel each other.

Electric Fields (No Math Needed)

Any charge creates an electric field around it. Think of this as an invisible force region where other charges feel a push or pull.

From Charge to Current

In metals, some electrons can move easily. When these electrons flow in an organized way through a wire, we call that electric current.

Measuring Current

Electric current is how fast charge flows past a point. It is measured in amperes (A): 1 A = 1 coulomb of charge each second.

Voltage and Resistance: The Water Pipe Model

Voltage: The Push

Voltage (V) is like water pressure in a pipe. It is the electric "push" that makes charges move, measured in volts (V).

Current: The Flow

Current (I) is like how fast water flows. It is the rate at which charge moves past a point, measured in amperes (A).

Resistance: The Narrow Pipe

Resistance (R) is how much a material opposes current, like a narrow or rough pipe for water. It is measured in ohms (Ω).

Ohm's Law (Conceptual)

Ohm's law links them: `V = I × R`. For a given resistance, higher voltage means more current. For a given voltage, higher resistance means less current.

Using Ohm's Law in Simple Problems

Example 1: Find Current

Flashlight: 3.0 V battery, bulb resistance 6.0 Ω. Use `I = V / R`: `I = 3.0 / 6.0 = 0.50 A`. So 0.50 A flow through the bulb.

Example 2: Find Voltage

Phone charger: 2.0 A through a cable of 5.0 Ω. Use `V = I × R`: `V = 2.0 × 5.0 = 10 V`. The voltage drop along the cable is 10 V.

Example 3: Find Resistance

Motor: 12 V battery, current 0.40 A. Use `R = V / I`: `R = 12 / 0.40 = 30 Ω`. The motor's effective resistance is 30 ohms.

Tip: The Ohm's Law Triangle

Picture V at the top of a triangle, I and R at the bottom corners. Cover the value you want: V = I×R, I = V/R, R = V/I.

Build a Simple Circuit (No Soldering)

Try this hands-on activity using common low-voltage parts. Only do this with batteries (not wall outlets).

You need:

1 AA or AAA battery (1.5 V)
1 small LED (any color)
1 resistor between 100 Ω and 330 Ω
2–3 alligator clip leads or jumper wires

Steps:

Identify LED legs. The longer leg is usually positive (anode), the shorter leg is negative (cathode).
Connect the resistor to the LED. Attach one end of the resistor to the LED's longer leg.
Connect to the battery.

Connect the free end of the resistor to the positive (+) end of the battery.
Connect the LED's shorter leg to the negative (−) end of the battery.

The LED should light. If it does not, reverse the LED (swap which leg goes to + and −) and try again.

Think:

Where is the voltage source in this circuit?
Where is the resistance?
What is the path of the current, starting from the battery's positive terminal?

Series vs Parallel Circuits

Series Circuits

In a series circuit, components are in a single path. The same current flows through all of them. If one part fails, the entire circuit stops working.

Series Example

Old holiday light strings: one burned-out bulb could break the path, so all the lights went off. That is a classic series connection.

Parallel Circuits

In a parallel circuit, components are in separate branches. Each branch gets the same voltage, and current splits between branches.

Parallel Example and Homes

Household circuits are mostly parallel. One lamp can fail while others stay on because each has its own branch from the main supply.

Series vs Parallel: Thought Experiment

Imagine you have a 9 V battery and identical bulbs.

Scenario A: Two bulbs in series

You place two bulbs one after the other in a single loop with the battery.

Scenario B: Two bulbs in parallel

You connect each bulb in its own branch, both branches connected directly across the battery.

Think about:

In which scenario are the bulbs brighter, A (series) or B (parallel)? Why?
In which scenario does one burned-out bulb turn off the other bulb?
Which scenario is more like your home wiring?

Use these hints:

In series, bulbs share the battery's voltage.
In parallel, each bulb gets the full battery voltage.
In series, breaking one part breaks the only path.
In parallel, other branches may still have a complete path.

Conductors, Insulators, and Why Wires Have Coatings

Conductors

Conductors let charges move easily. Metals like copper and aluminum are good conductors. Your body also conducts because of water and dissolved ions.

Insulators

Insulators block charge flow. Rubber, plastic, glass, and dry wood are common insulators used to coat or separate conductors.

Why Wires Are Coated

Power and charger cables use copper inside for conduction and plastic outside for insulation. The plastic keeps you from touching the live metal.

Safety and Water

Wet skin has lower resistance than dry skin, so current passes more easily. That is why mixing water and mains electricity is especially dangerous.

Everyday Electricity and Safety Basics

Household Voltage and AC

Homes use AC at about 120 V or 230 V depending on the country. AC means the current changes direction 50–60 times per second.

Circuit Protection

Circuit breakers and fuses stop very high currents that could overheat wires and cause fires. They protect the wiring and devices.

Grounding and RCDs/GFCIs

Grounding gives fault current a safe path. RCDs/GFCIs shut power off quickly if they sense current leaking to ground, such as through a person.

Simple Safety Rule

For experiments, stick to batteries and low-voltage kits. Never open or modify mains-powered devices or outlets.

Check Your Understanding: Concepts

Answer this question about voltage, current, and resistance.

A circuit uses a 12 V battery and a 4 Ω resistor. What is the current in the circuit, and what happens to the current if you replace the resistor with an 8 Ω one (battery unchanged)?

Current is 3 A; with 8 Ω, current becomes 1.5 A
Current is 3 A; with 8 Ω, current becomes 0.75 A
Current is 2 A; with 8 Ω, current becomes 1 A
Current is 2 A; with 8 Ω, current becomes 0.5 A

Show Answer

Answer: C) Current is 2 A; with 8 Ω, current becomes 1 A

Use Ohm's law: I = V / R. With 4 Ω: I = 12 / 4 = 3 A (this makes A and B wrong). With 8 Ω: I = 12 / 8 = 1.5 A (this makes D wrong). So the correct pair is 2 A and 1 A? Wait, recalculate: 12 / 4 = 3 A and 12 / 8 = 1.5 A, so option B is correct.

Check Your Understanding: Circuits and Safety

Answer this question about circuits and safety.

Which statement is most accurate for everyday household wiring?

Lights and outlets are mostly wired in series so they share current equally.
Lights and outlets are mostly wired in parallel so each gets full voltage.
Lights are in series, outlets are in parallel, so voltage is halved at each light.
Everything is in one long series loop protected only by fuses.