Circuits and Electric Current

Electric Current

• Electric current is the amount of charges (electrons) flowing per second.
• Wires are commonly made of copper.
• Copper wire contains copper ions surrounded by electrons.
• Electrons move along the wire when pushed by an external source, like a battery.

Measuring Electric Current

• An ammeter measures electric current.
• The unit of electric current is Ampere (A).

Series Circuits

• In a series circuit, electrical components (like light bulbs) are linked one after the other.
• There is a single path for the flow of current.

Parallel Circuits

• In a parallel circuit, electrical components (like light bulbs) are linked across one another
• The paths are branched for the flow of current in a parallel circuit, establishing multiple loops.

Connecting an Ammeter in a Circuit

• Connect the ammeter in series.
• Connect the positive terminal of the ammeter to the positive terminal of the battery.
• Connect the negative terminal of the ammeter to the negative terminal of the battery.

Current Flow in Series and Parallel Circuits

• In a series circuit, the current is the same throughout the circuit.
• If one light bulb is broken in a series circuit, the circuit is broken, and all light bulbs will be off.
• In a parallel circuit, the total current is the addition of all the current in the different branches.
• In a parallel circuit, if one light bulb is broken or blown, the current can still flow through the other branch, meaning the other light bulb will still be on.

Controlling Current Flow with Switches in Circuits

• With series circuits, all lightbulbs cannot be turned on and off separately and the switch in the circuit can turn them all on or turn them all off.
• With parallel circuits, the light bulbs can be turned on and off separately and a switch in each branch controls the lamps in that branch.

Voltage or Potential Difference

• The voltage is a measure of the strength of a cell or battery used to send a current around the circuit.
• In an electrical circuit, the battery pushes electrons to flow, and the electron gains electrical energy.
• The size of the pushing force depends on the voltage
• More batteries result in more voltage, leading to a more pushing force, more electron flow, more electrical energy, and ultimately, more current.
• More current will yield a brighter lamp
• The symbol for voltage is V.
• The SI unit of voltage is Volt (V).

Measuring Voltage or Potential Difference

• A voltmeter is used to measure the voltage across the components.
• To measure the voltage across a light bulb, place the voltmeter across the light bulb.
• To measure the voltage across the electrical cell, place the voltmeter across the cell.

Voltage in Series Circuits

• The voltage across the components equals the voltage of the battery.
  • V = V1 + V2

Voltage in Parallel Circuits

• Each branch is connected directly to the cell.
• The voltage across the bulbs is the same as the voltage across the cell.
  • V = V1 = V2

Series vs Parallel Circuits

• In a series circuit, the current is the same throughout the circuit | = |1= |2
• In a series circuit, the voltage across the components adds up to the voltage of the battery V = V1 + V2
• In a series circuit, a switch can turn them all on or turn them all off.
• In a parallel circuit, total current is the addition of all the current in different branches | = 1+2
• In a parallel circuit, the voltage across the bulbs is the same as the voltage across the cell V = V1 = V2
• In a parallel circuit, the switch in each branch controls the lamps in that branch.

Resistance

• Resistance measures how much a material opposes the flow of current.
• The symbol for resistance is R and is measured in Ω (Ohms)
• More light bulbs means the lights bulbs are dimmer
• When electric resistance is high, this makes it difficult for current to flow through the wire.
• A high resistance leads to a smaller current.
• Light bulbs act as resistance against the flow of current.
• A resistor is a device sometimes used to make light dimmer or brighter, depending on usage.

Resistance in Cylindrical Conductor (Wire)

• Resistance is directly proportional to the length of the wire.
• Resistance is inversely proportional to the surface area of the wire.
• Resistance also depends on the types of material of the wire.

Calculating Resistance

• Resistance(R) = Voltage (V) / Current (I)
• The SI unit of resistance is Ohm (Ω)
• The SI unit of voltage is Volt (V)
• The SI unit of current is Ampere (A)

Specific Resistance Calculation Example

• In a series circuit, the current is the same throughout.
• If the current passing through a buzzer is 0.1A, and it is the only component in the circuit.
• If the voltage of the battery equals the voltage across the buzzer and is 6V, then:
• Resistance (R) = Voltage (V) / Current (I) = 6 / 0.1 = 60 Ω