GCSE    Resistors    Questions 0 to 27   -->  View All  

This circuit divides the voltage in the same ratio as the resistors so V₁ / V₂   =   R₁ / R₂   and   V₂   =  V_s R₂ / (R₁ + R₂)    where Vs is the supply voltage.

R1 and R2 form a Voltage Divider. Usually one of these is variable and used to sense light, temperature, position, pressure etc.

The light sensing circuit turns on the lamp when it gets dark. A Schmitt trigger NOT gate should be used.

The voltage is divided in the ratio of the resistor values (assuming the current is the same in both resistors).

Two or more resistors in series can be used to set a required voltage at a point in a circuit. For example, this could correspond to

• a threshold voltage at which an alarm should sound
• the voltage output required from a power supply circuit
• the volume needed from a radio
• the speed at which a fan runs.

V₂ = V_s R₂ / (R₁ + R₂)    where Vs is the supply voltage.

V₁ = V_s R₁/ (R₁ + R₂)    where Vs is the supply voltage.

V₁ / R₁ = V₂ / R₂        or        V₁ / V₂ = R₁ / R₂        also        V₁ + V₂ = V_s

In this simulation, the resistors add up to 12kΩ and the voltage is 12 Volts.
This makes the maths stupidly simple.
Each "k" of resistance has one volt across it. Simples!
Click the switch to turn on the circuit.