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Exercises: Voltage dividers

Calculate on paper or use the simulator, then enter your result. Close this panel to measure; the Exercises tab reopens it.

How to solve

With no load on the output, Vout = Vin × R2/(R1 + R2). R2 is the lower resistor. Select R2 in the simulator to measure its voltage.

Exercise 1

Source: 12 V. R1 = 10 kΩ; R2 = 10 kΩ

What is the voltage across R2?

Exercise 2

Source: 9 V. R1 = 2.2 kΩ; R2 = 1 kΩ

What is the voltage across R2?

Exercise 3

Source: 5 V. R1 = 1 kΩ; R2 = 2 kΩ

What is the voltage across R2?

Help

The whole screen is a board of dots. Every part has two or three leads, and anything touching the same dot is connected, just like on a breadboard. The circuit is solved again after every change: LEDs light up, the motor spins, yellow arrows show the path and direction of the current, and the multimeter measures whatever part you tap.

Capacitors, inductors and the signal generator make the circuit run in time: you can watch a capacitor charge, a flasher blink and the waveform on the oscilloscope, even in slow motion. An LED without a resistor burns out (above 30 mA), a resistor running past its power rating heats up and burns above twice that, and the fuse sacrifices itself to protect the rest, just like in real life. The circuit is saved on this device, and you can download the file or the image, or copy a link to send to someone.

How to use

Open Parts and tap a part to drop it in the middle of the board, or drag it where you want it.
Drag a part to move it; the wires attached to it follow. Drag an empty spot to pan, and use the mouse wheel (or two fingers) to zoom.
To add a wire, drag from one dot to another (or tap a dot, then the point where the wire should end). A wire ending in the middle of another one makes a T junction.
Tap a part to measure it, change its value and see its calculator. Tap a switch to turn it on and hold a push button to press it.
Examples has ready-made circuits: a flasher, a transistor switch, a capacitor, a rectifier and more.

Frequently asked questions

Is the circuit simulator free?

Yes. It runs right in your browser, on desktop and on mobile, with no sign-up and nothing to install. The circuit is saved on your device, and you can download the file or copy a link to open it elsewhere.

Which parts can I use?

Battery, signal generator, ground, resistor, potentiometer, capacitor, inductor, LED, diode, zener, NPN and PNP transistors, lamp, motor, buzzer, switch, push button, fuse, voltmeter and ammeter.

How does the simulator solve the circuit?

After every change it solves the whole circuit with Kirchhoff's laws (nodal analysis), not just series and parallel. LEDs and diodes have a fixed voltage drop, the transistor has a gain β, and capacitors and inductors are computed step by step in time.

Why did my LED burn out?

An LED burns out above 30 mA, just like in real life. Connected straight to the battery, with no resistor, too much current flows. Add a series resistor: the LED resistor calculator, which opens when you tap the LED, gives you the value.

Can I simulate AC and see the waveform?

Yes. The signal generator makes sine, square, triangle and pulse waves, and the oscilloscope plots the voltage or current of up to four parts over time, even in slow motion.

Is it like Falstad, PhET or Tinkercad?

The idea is similar: build a circuit and see it work. Here it opens instantly on your phone, every part tells you what's happening to it, and Ohmpal's calculators are right beside it.

Keyboard shortcuts

R: Rotate the part (Shift+R rotates the other way)
F: Flip (swaps + and −, or collector and emitter)
Delete: Delete the selection
Ctrl+Z / Ctrl+Y: Undo and redo
Ctrl+C / Ctrl+V / Ctrl+D: Copy, paste and duplicate
Ctrl+A: Select all
Shift + drag: Select several parts with a box
Arrow keys: Move the selection (or the board)
+ / − / 0: Zoom in, zoom out and fit to screen
Space: Pause and resume time
Esc: Deselect or cancel the wire