# Day 113

## Current

• Rate at which charge flows through a surface I=Q/t, where I=current;Q=charge; t= time
• I is measured in Amperes (A) = 1C/s
• Analogy: rate at which blood flows through a vein or artery
• Current direction convention is to give the current flow the same direction as the flow of positive charges Therefore, current flows from the positive to the negative terminal of a battery

## Voltage

• The battery provides the emf in the circuit
• Emf = electromotive force; another term for potential difference or voltage; measured in Volts (V)
• Analogy: the heart provides the flow of blood just as the battery provides the flow rate of charges (current) in the circuit
• The heart/artery/vein system is a closed system just like an electric circuit

## Resistance

• Provides a deterrent to the flow of current in the circuit
• Resistors are used to reduce the amount of current
• At a constant voltage, R and I are inversely related
• Analogy: Plaque build-up in the artery inhibits blood flow
• Resistors can be fixed or variable in a circuit
• Examples of appliances with variable resistors: toaster, iron, hairdryer. Resistance occurs because the electrons are restricted by the walls of the wires

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