Direct Current Circuits

Question 1

Conservation of charge

Answer 1

Electrical charge is conserved – electrons cannot be created or destroyed inside a material.

Question 2

Kirchhoff’s First Law

Answer 2

The algebraic sum of the currents at a junction is 0.

Question 3

Conservation of energy

Answer 3

In a period of time, the quantity of electrical energy generated within the cell is equal to the heat energy dissipated by the resistor.

All energy produced by a cell is dissipated in the external load resistor and the cell’s internal resistance.

Question 4

Resistors in series

Answer 4

Question 5

Resistors in parallel

Answer 5

Question 6

Potential Divider

Answer 6

Allows a fraction of the p.d. to be supplied to an external circuit.

V_out = R₁V_in/(R₁ + R₂)

Fixed resistors - output voltage is invariable

Rheostat - continuously variable potentiometer

The output voltage is connected across a load resistor.

Question 7

Effect of loading on V_OUT

Answer 7

Voltage across the load decreases as load resistance decreases.

If the load is infinite, then V_out is at its maximum.

If the load is 0, then V_out is 0