Direct Current Circuits

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

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Potential Divider

• Remember Series

• Fixed Resistor
• Equation for output voltage

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Potential Divider

• Variable Resistor
• Potentiometer
• Rheostat
• Light Dependent Resistor
• Resistance depends on the amount of light on it
• Thermistor
• Resistance depends on the temperature

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Light Dependent Resistor (LDR)

• Resistance decreases as light intensity increases

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Thermistor (NTC)

• Resistance decreases as temperature increases

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Potentiometer

• Resistance varies with length of resistor

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Circuit Laws

• Kirchhoffs Junction Rule
• The total current in a junction is zero
• Conservation of Charge

• Current going in
• Current leaving -

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Circuit Laws

• Kirchhoffs Loop Rule
• 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

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Loop Rule
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Example 1

• Find the current, I

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Example 2

• Find the current, I
• The internal resistance, r
• The emf, e

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Example 3

• Find the current in the middle branch
• The unknown emf