1. Direct Current Circuits
Series and Parallel Circuits
Potential Divider
Circuit Laws
Direct Current Circuits

2. Series Circuit

3. Parallel Circuit

4. Examples Question 15.6, page 269 For the same question, calculate
The current in each resistor
The pd across each resistor if the total voltage across the circuit is 100 V

5. Potential Divider Remember Series Fixed Resistor
Equation for output voltage

6. Potential Divider Variable Resistor Potentiometer Rheostat
Light Dependent Resistor
Resistance depends on the amount of light on it
Thermistor
Resistance depends on the temperature

7. Light Dependent Resistor (LDR)
Resistance decreases as light intensity increases

8. Thermistor (NTC)
Resistance decreases as temperature increases

9. Potentiometer
Resistance varies with length of resistor

10. Circuit Laws Kirchhoff’s Junction Rule Current going in +
The total current in a junction is zero
Conservation of Charge
Current going in +
Current leaving -

11. Circuit Laws Kirchhoff’s Loop Rule For emf sources:
The total voltage in a loop is zero
Conservation of Energy
For emf sources:
Traversing from – to +, positive
For resistors, V = IR:
If assumed or given current direction is the same as assumed or given loop direction, negative

12. Loop Rule

13. Example 1
Find the current, I

14. Example 2
Find the current, I
The internal resistance, r
The emf, ε

15. Example 3
Find the current in the middle branch
The unknown emf