Virtual laboratory/Physics/Electricity/Ohm's law — the formula I = U/R, voltage, resistance, current

Ohm's law — the formula I = U/R, voltage, resistance, current

What we'll do: We'll build a simple circuit and change the voltage and resistance, checking how they control the current and the brightness of the bulb.

What you see on screen: A circuit diagram with a battery, a resistor and a bulb, sliders for voltage U and resistance R, and electrons flowing along the wire whose stream thickens as the current grows. The relation bar shows I = U/R. Readouts: U, R, current I and power P.

Ohm's law — the formula I = U/R, voltage, resistance, current
Physics · Electricity · Ohm’s law (FIZ.PRAD.PP.03)
Source voltage UU6.0 V
Resistance RR100 Ω
You double the resistance R at constant voltage — the current:
voltage U
6.0 V
resistance R
100 Ω
current I
0.060 A
power P
0.36 W
🎯 Challenge: hit the current
streak: 0

I’ll give you a target current — tune the voltage and resistance to reach it. I = U/R.

What just happened?

You doubled the resistance and the current dropped by half. At constant voltage the current and resistance are inversely proportional.

Ohm’s law:

I=URI = \dfrac{U}{R}

— the current is directly proportional to the voltage and inversely proportional to the resistance. U — voltage (V), R — resistance (Ω), I — current (A).

What does it mean in practice?

Higher voltage “pushes” the charges harder → more current. Higher resistance hinders the flow → less current. Hence:

U=I⋅RR=UIU = I\cdot R \qquad R = \dfrac{U}{I}

Why do wires and fuses heat up?

Current flows through the resistor and power P=U⋅IP = U\cdot I is released — the larger the current, the more heat. That is why a thin, heavily loaded wire heats up.

Why you need this for the exam:

I = U/R plus P = U·I solve most problems about simple circuits. Trick: write down what is constant (U or R) and see how I changes.

Remember: the current rises with voltage and falls with resistance — I = U/R. It is the foundation of all electricity.

Illustrative model · NexTutor Virtual laboratory

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Theory & formulas

Ohm's law

I=URI = \dfrac{U}{R} The current is directly proportional to the voltage and inversely proportional to the resistance.

What follows

  • at constant UU: larger RR → smaller current,
  • at constant RR: larger UU → larger current.

Power

P=UI=I2R=U2RP = UI = I^2 R = \dfrac{U^2}{R} Flowing current releases power converted into heat — that is why wires heat up.

Symbols: II — current, UU — voltage, RR — resistance, PP — power.

Frequently asked questions

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What does Ohm's law state?

The current is directly proportional to the voltage and inversely proportional to the resistance: I = U/R.

›

What happens to the current when the resistance rises?

It decreases — at constant voltage the current is inversely proportional to the resistance.

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Why do wires heat up?

Because the flowing current releases power P = U·I converted into heat; more current = more heat.

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