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Electric Circuits
Components of a Circuit
Switch: controls the current that flows through the circuit
Cells and Batteries: power sources, measured in voltage (V)
Light Bulb: represented by a circle and a cross, light source in the circuit
Voltmeter: measures the voltage flowing through the circuit
Ammeter: measures the current flowing through the circuit
Resistor: controls the amount of current flowing through the circuit
Rheostat: variable resistor
Motor: can be included in a circuit to carry out work
Power Sources
"A power source is a device that supplies energy to a circuit."
Measured in voltage (V)
Unit symbol: V
Measured using a voltmeter, connected in parallel to the component
Current
"Current is the flow of electric charge or electrons through a certain point
of a circuit."
Measured in amperes (A)
Unit symbol: A
Represented by the symbol: I
Measured using an ammeter, connected in series in the circuit
Resistance
"Resistance is the ability of a conducting material to control the amount of
current flowing through or to provide a useful energy transfer."
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Measured in ohms (Ω)
Unit symbol: Ω
Represented by the symbol: R
Opposition to the flow of electric charge
Series Circuits
Only one pathway for current to flow through
Current is equal everywhere in the circuit
Potential difference (voltage) is the sum of the voltages in the circuit
More resistors in series increase the total resistance
Resistors in series are potential dividers
Formulas for Series Circuits
Formula Description
I_T = I_1 = I_2 = I_3 Current is equal everywhere in the circuit
V_T = V_1 + V_2 + V_3 Potential difference is the sum of the voltages in the circuit
R_T = R_1 + R_2 + R_3 Total resistance is the sum of the individual resistances
Parallel Circuits
Multiple pathways for current to flow through
Current divides between the different parts of the circuit
Potential difference (voltage) is equal everywhere in the circuit
More resistors in parallel decrease the total resistance
Resistors in parallel are current dividers
Formulas for Parallel Circuits
Formula Description
I_T = I_1 + I_2 + I_3 Total current is the sum of the individual currents
V_T = V_1 = V_2 = V_3 Potential difference is equal everywhere in the circuit
1/R_T = 1/R_1 + 1/R_2 + Total resistance is calculated using the reciprocal of the
1/R_3 individual resistances
Triangle Formulas
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VIR Triangle
Formula Description
V=I×R Voltage is equal to current multiplied by resistance
I=V÷R Current is equal to voltage divided by resistance
R=V÷I Resistance is equal to voltage divided by current
QIT Triangle
Formula Description
Q=I×T Charge is equal to current multiplied by time
I=Q÷T Current is equal to charge divided by time
T=Q÷I Time is equal to charge divided by current
PVI Triangle
Formula Description
P=V×I Power is equal to voltage multiplied by current
V=P÷I Voltage is equal to power divided by current
I=P÷V Current is equal to power divided by voltage
WVQ Triangle
Formula Description
W=V×Q Work or energy is equal to voltage multiplied by charge
V=W÷Q Voltage is equal to work or energy divided by charge
Q=W÷V Charge is equal to work or energy divided by voltage
Calculating Total Voltage
In a series circuit, the total voltage is the sum of the individual voltages. The formula
for calculating total voltage is:
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VT = V1 + V2 + ... + Vn
Where VT is the total voltage and V1, V2, ..., Vn are the individual voltages.
Circuit Component Voltage
Voltmeter 1 5V
Voltmeter 2 4V
Total Voltage 9V
Calculating Total Resistance
In a series circuit, the total resistance is the sum of the individual resistances. The
formula for calculating total resistance is:
RT = R1 + R2 + ... + Rn
Where RT is the total resistance and R1, R2, ..., Rn are the individual resistances.
Circuit Component Resistance
Light Bulb 1 2 ohms
Light Bulb 2 3 ohms
Total Resistance 5 ohms
Calculating Total Current
In a series circuit, the total current can be calculated using the formula:
I = V/R
Where I is the total current, V is the total voltage, and R is the total resistance.
Circuit Component Value
Total Voltage 9V
Total Resistance 5 ohms
Total Current 1.8 amperes
Parallel Circuits ️
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Calculating Total Voltage
In a parallel circuit, the total voltage is the same across all components. The formula
for calculating total voltage is:
VT = V1 = V2 = ... = Vn
Where VT is the total voltage and V1, V2, ..., Vn are the individual voltages.
"The voltmeter reading or the potential difference is equal everywhere in
a circle."
Circuit Component Voltage
Voltmeter 1 6V
Voltmeter 2 6V
Total Voltage 6V
Calculating Total Resistance
In a parallel circuit, the total resistance can be calculated using the formula:
1/RT = 1/R1 + 1/R2 + ... + 1/Rn
Where RT is the total resistance and R1, R2, ..., Rn are the individual resistances.
Circuit Component Resistance
Light Bulb 1 3 ohms
Light Bulb 2 1 ohm
Total Resistance 0.75 ohms
Calculating Total Current
In a parallel circuit, the total current can be calculated using the formula:
IT = I1 + I2 + ... + In
Where IT is the total current and I1, I2, ..., In are the individual currents.
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Circuit Component Current
Ammeter 2 5A
Ammeter 3 3A
Total Current 8 amperes
Alternatively, the total current can be calculated using the formula:
I = V/R
Where I is the total current, V is the total voltage, and R is the total resistance.
Circuit Component Value
Total Voltage 6V
Total Resistance 0.75 ohms
Total Current 8 amperes
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