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Key Concepts of Circuits

Series Circuits

• Elements connected in a line along the same conductor.

• Total resistance: Equal to the sum of individual resistances (R_total = R1 + R2 + R3).

• Current: The current through each circuit element is the same as the total current (I = I1 = I2 = I3).

• Voltage: The sum of the voltages across each circuit element equals the total circuit voltage (V_total = V1 + V2 + V3).

• Example of Series Circuit: Christmas lights. If one bulb goes out (bad bulb), the entire string goes out due to one wire connecting all.

Parallel Circuits

• Elements connected at their ends, allowing multiple pathways for current to flow.

• Total current: The sum of the currents through each circuit element equals the total circuit current (I_total = I1 + I2 + I3).

• Voltage: Voltage across each circuit element is the same and equal to total circuit voltage (V_total = V1 = V2 = V3).

• Total resistance: Calculated as the inverse of the sum of the reciprocals of each individual resistance (1/R_total = 1/R1 + 1/R2 + 1/R3).

• Example of Parallel Circuit: If one bulb goes out, the other bulbs remain lit.

Differences Between Series and Parallel Circuits

• Voltage in Series: The sum of voltages equals the total voltage.

• Voltage in Parallel: Voltage remains the same across each element.

• Current in Series: Same throughout all components.

• Current in Parallel: Total current is the sum of individual currents.

• Resistance in Series: Resistance adds up.

• Resistance in Parallel: Use reciprocal formula.

Closed vs Open Circuits

• Closed circuit: A complete path allowing electricity to flow (e.g., light switch on).

• Open circuit: A break in the pathway preventing electricity flow (e.g., light switch off).

Types of Current

Alternating Current (AC)

• Pulsates back and forth, used in homes.

• Typical voltage: around 120 or 220 volts.

• Frequency: 60 cycles per second.

Direct Current (DC)

• Flows in one direction, used in devices like batteries and X-ray tubes.

Electrical Power

• Electrical power (P) calculated using the formula: P = I × V

  • Where I = current (in amperes), V = voltage.

• Example Calculation:

  • If an appliance uses 12 amps at 120 volts, then power used = 12 A × 120 V = 1440 watts.

  • If a clothes dryer uses 35 amps at 220 volts, then power used = 35 A × 220 V = 7700 watts.

• The bulb with lower wattage (60 watts) has higher resistance than a higher wattage bulb (100 watts), which is brighter due to lower resistance allowing more current flow through.

Protecting Electrical Devices

• Use of fuses or circuit breakers to prevent overload.

• Circuit breakers: Reusable protective devices found in homes and labs.

• Ground connections: Direct excess electricity safely into the ground, which absorbs it.

  • Grounding prevents electrical shock and system failure.

Short Circuits

• Occur when resistance is unexpectedly lowered, resulting in increased current.

• Potentially dangerous; can cause overheating or fire.

• Safety measures: Circuit breakers or fuses should intervene to cut off the current flow.