Ohm’s Law

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Slide 1  Ohm’s Law
 Voltage, Current & Resistance

Slide 2  Current
 An electrical current is the flow of electrons through a complete circuit.
 The brightness of a light bulb is an indicator of the amount of current (or flow) through the bulb.
 The unit of current is the Ampere (A) or “amp” for short.

Slide 3  The amount of current that flows in a circuit depends on the resistance of the circuit and the voltage of the source.
 * In other words, a battery does not supply a constant amount of current.
 Current is Variable

Slide 4  Voltage
 Voltage is the push that drives flow of electrons.
 Voltage in a circuit is determines by the source
 * Batteries will also supply a set amount of voltage (ex. 1.5V, 9V, 12V)
 The unit of voltage is the Volt (V).

Slide 5  Electrical Potential Energy
 Voltage is the result of a difference in electrical potential energy.
 This is similar to gravitational potential energy, which makes balls roll down hills.
 In this case charges flow from areas of high potential to low potential.

Slide 7  Resistance
 Resistance is an obstacle to the flow of electrons.
 The total resistance of the circuit impacts the amount of current in the circuit.
 The unit of resistance is the Ohm (Ω).

Slide 8  Insulators & Conductors
 Different materials and objects have different resistances
 Some objects have a set resistance – like nichrome wire
 Some objects have a variable resistance – like a lightbulb, which has a different resistance when cold v. hot.
 The resistance of an object depends on how tightly the atoms hang on to their electrons.

Slide 10  Ohm’s Law
 “The current flow through a conductor is directly proportional to the potential difference and inversely proportional to the resistance.”
 In other words: V = IR any of these three values can be found as long as the other two are known.

Slide 11  Resistance in a Circuit
 When elements are added in series, their total resistance is equal to the sum of their individual resistances:
 Each bulb has a resistance of 0.2 Ω.
 The wire and switch have insignificant resistance.
 What is the total resistance of the circuit?

Slide 12  0.5 Ω
 0.3 Ω