Current, Resistance, and Ohm's Law

Current, Resistance, and Ohm's Law

By Rachel Wampler

Current

Multiple Choice

Small computer speakers often have power supplies that give 12 VDC at 200 mA. How much energy charge flows through the circuit in 1 hour and how much energy is used to deliver this charge?

• 720 C

  8640 J

• 0.2 C

  8640 J

• 720 C

  2.4 J

• 0.2 C

  2.4 J

Conventional Current

• Electrons are the charge that flows through wires

• Historically thought positive charges move

• Conventional current → imaginary flow of positive charges

  • Flows from positive terminal and into negative terminal (a)

  • Real current flows the opposite way​ (b)

Drift Velocity

Resistance, Current, and Voltage

• Think of water pumps

  • Bigger pumps → more water flowing

  • Skinny pipes (more resistance) → less water flowing

• Electrical circuits

  • Bigger battery voltage → more current

  • Big electrical resistance →less current​

Ohm's Law

• V = ɛmf

• I = Current​

• R = Resistance

  • Unit: V/A or ohm ​(Ω)

​

Resistors

• Device that offers resistance to the flow of charges

• Copper wire has very little resistance

• Symbol used for a in a circuit diagram

  • Resistor

  • Wire​

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Multiple Choice

Our speakers use 200 mA of a current at maximum volume. The Voltage is 12 V. The current is used to produce a magnetic field which is used to move the speaker cone. Find the resistance of the electromagnet.

• 0.017 Ω

• 2.4 Ω

• 60 Ω

• -2.4 Ω