L28. Voltage, Current, and Resistance

Electricity

R-report

L28. Voltage, Current, and Resistance

How do a battery's 'push' and a wire's 'slow-down' decide how bright a bulb shines?

Voltage: the electrical push

Voltage is the amount of electric potential energy given to each tiny charge by a source like a battery. Think of voltage as how strongly the battery can push charges around a circuit. We measure voltage in volts (V). A higher voltage can move charge through a circuit more strongly than a lower voltage, but voltage alone doesn't guarantee a big flow — it’s the push that can produce flow if the path allows it. You already learned about electric current (the flow of charge). Voltage is the reason current can flow; it provides the energy change per charge that makes current possible. A simple way to notice voltage: a new AA (about 1.5 V) will usually make a small flashlight bulb glow less brightly than a 9 V battery in the same bulb holder designed for higher voltage.

Resistance: what slows current

Resistance is a property of any material or component that makes it harder for charge to move. More resistance means less current for the same push (voltage). We measure resistance in ohms (Ω). Different objects and conditions change resistance. The idea of resistance explains why a thin wire gets hotter than a thick wire carrying the same current, and why heating elements glow rather than letting current pass easily.

• Material: metals like copper have low resistance; rubber and glass have high resistance. Shape: longer or thinner pieces of the same material have more resistance. Temperature: for most metals, resistance increases as temperature rises. Components: resistors are parts made to add a known amount of resistance to a circuit.

Putting them together: a short classroom investigation

Ohm's law links these ideas: for many simple circuits, voltage (V) equals current (I) times resistance (R) — V = I × R. That means if you increase voltage with the same resistance, current goes up. If you increase resistance with the same voltage, current goes down. Try this safe, short investigation with your teacher's permission to see those relationships happen with a small flashlight bulb, two AA batteries, and a multimeter if available.

• 1) Build a simple circuit: a battery holder with one AA and a small bulb (or a classroom bulb holder). Note how bright the bulb is. 2) Replace the single AA with two AA batteries in series (more voltage) and observe: the bulb should glow brighter if the bulb can take the extra voltage. 3) Return to one AA and add a small resistor or a long thin wire segment in series; observe: the bulb should dim because the added resistance lowers the current. 4) (Optional) Use a multimeter to measure voltage across the battery and current through the bulb to see V and I numbers and check V = I × R roughly holds.

Big picture

Voltage is the push that can make charge move; current is the movement itself; resistance is what gets in the way. Ohm’s law (V = I × R) links them and helps predict what will happen when you change one part of a simple circuit.

In everyday devices you can change brightness, heating, or motor speed by changing the voltage available or the amount of resistance in the path. Internal resistance inside batteries and the physical shape and material of wires and components all matter in those changes.