Series and Parallel Circuits

• Electrical components can be connected in series or parallel.

Current in Series Circuits

• A series circuit has only one loop or path for electrons to flow.
• In a series circuit, the current has the same value at any point.
• The amount of current depends on the voltage of the power source.
• It also depends on the number and type of components.
• Increasing the voltage of the power source increases the current.
• Increasing the number of components increases the total resistance, which reduces the current.

Current in Parallel Circuits

• A parallel circuit has two or more loops or paths for electrons to take.
• Parallel circuits contain junctions and branches, where junctions are points where two or more wires meet.
• Branches are the sections of wire between junctions.
• In a parallel circuit, the current has different values at different points.
• The sum of the currents in individual branches equals the total current before and after the branches.
• At a junction, current is always conserved, meaning the amount flowing in equals the amount flowing out.
• Current doesn't always split equally; it depends on the resistance of components along each branch.
• If the resistance is identical in each branch, the current will be identical.
• Electrons, or any charge, cannot be created or destroyed.

Voltage in Series Circuits

• The total voltage of a power supply is shared among components.
• For identical components, the voltage across them will be the same and equal to half the total voltage.
• If there are different values of resistance, the voltage will be higher across components with higher resistance and lower across those with lower resistance.

Voltage in Parallel Circuits

• In a parallel circuit, the total voltage across each branch is the same as the voltage of the power supply.
• Lamps connected in parallel have the same voltage across them.

Series Circuit Advantages

• All components are controlled by a single switch.
• Fewer wires are required.

Series Circuit Disadvantages

• Components cannot be controlled separately.
• If one component breaks, all other components stop working.

Parallel Circuit Advantages

• Components can be individually controlled using their own switches.
• If one component breaks, the others will continue to function.

Parallel Circuit Disadvantages

• It can be more complicated to set up, because, many more wires are involved.
• All branches have the same voltage as the supply.
• Which makes it more difficult to voltage across individual components.

Resistors in Series

• When two or more resistors are connected in series, the total resistance is equivalent to the sum of their individual resistances.
• R = R1 + R2
  • R is the total resistance, in ohms (Ω)
• Increasing the number of resistors increases the overall resistance.
• The total voltage is the sum of the voltages across each of the individual resistors.

Series Circuits Summary

• The current is the same at all points and in each component.
• The voltage of the power supply is shared between the components.
• The total resistance is the sum of the resistances of each component.

Parallel Circuits Summary

• The current from the supply splits in the branches.
• The voltage across each branch is the same.
• The total resistance is less than that of each component.

IV Graphs

• To investigate the relationship between current and voltage different components, the following equipment is required:
  • Ammeter
  • Voltmeter
  • Variable Resistor
  • Power Source
  • Wires
• The relationship between current and voltage can be shown on an IV graph.
• When the voltage across a component is varied, the current flowing through it may vary linearly or non-linearly.
• When the relationship between current and voltage is linear:
• The IV graph is a straight line which passes through the origin.
• The resistance is constant.
• When the relationship between current and voltage is non-linear:
  • The IV graph that is not a straight line.
  • The resistance is not constant.

IV Graph - Wire/Fixed Resistor

• The relationship between current and voltage for a wire or fixed resistor is directly proportional.
• The IV graph is a straight line, so voltage and current increase (or decrease) by the same amount and the slope of the graph is constant, so resistance is constant.

IV Graph - Filament Lamp

• The current is directly proportional to the potential difference (voltage).
• As the voltage increases and the temperature of the filament increases:
  • The atoms in the metal lattice of the filament vibrate more, which causes an increase in resistance.
  • This makes it more difficult for free electrons to pass through causing a slower rate in the current increase.

IV Graph - Diode

• A diode allows current to flow in one direction only which is called forward bias.
• In the reverse direction, the diode has very high resistance, and therefore no current flows.
• This is called reverse bias.
• The IV graph is shown by a sharp increase in voltage and current when the diode is in forward bias, showing the resistance is very low.
• When the diode is in reverse bias on the IV graph:
  • There is a zero-current reading.
  • The resistance is very high.

Resistance

• Resistance is the opposition to the flow of current.
• The higher the resistance of a circuit, the lower the current.
• Resistors come in two types: fixed and variable.
• Fixed resistors have a constant resistance.
• Variable resistors can change the resistance by changing the length of wire that makes up the circuit.
• A longer length of wire has more resistance than a shorter length of wire.

Thermistors

• Environmental conditions, such as temperature and light intensity, can influence the resistance of components like:
  • Thermistors.
  • Light-dependent resistors (LDRs).
• The resistance of a thermistor depends on its temperature.
• The resistance of a thermistor is high in cold conditions and low in hot conditions.
• The resistance of a thermistor decreases as the temperature increases.
• The resistance of a thermistor increases, as, the temperature decreases, the resistance of a thermistor increases

LDRs

• The resistance of a light-dependent resistor (LDR) depends on the light intensity on it.
• The resistance of an LDR is high in dark conditions and low in bright conditions.
• The higher the light intensity, the lower the resistance of an LDR.
• As the light intensity decreases, the resistance of an LDR increases.

LEDs

• Lamps and light-emitting diodes (LEDs) illuminate (light up) when current flows through them
• LEDs are a type of diode, which means they only allow current to flow through them in one direction
• Therefore, in a circuit, an LED will only light up if it is placed in the correct direction:
  • LEDs can be used to indicate the presence of a current because they illuminate when current flows through them
  • Lamps act similarly

Explore series and parallel circuits. Learn about calculating total resistance, current, and voltage distribution in each type of circuit. Problems on calculating equivalent resistance are included.