8.3Resistance and Ohm’s LawName:

Date:

Block:

(Reference: BC Science 9 pp. 290 - 301)

RESISTANCE AND THE FLOW OF ELECTRONS

  • resistance: ______

______

  • Ex. The ______resistance of the filament of a light bulb causes the electrons’ electrical energy to be transformed into light and heat energy.
  • In the lab last class, the filament of the light bulbsresisted the flow of electrons and therefore ______current.
  • You observed that the higher the voltage of the bulb, the ______the current.
  • The conducting wire has very ______resistance and not much energy is lost to the wire.

RESISTANCE AND CURRENT

Remember, ______isthe difference in potential energy per unit of charge between two different points in a circuit, and ______is the amount of charge passing a point in a conductor per second.

Voltage across the source is ______proportional to current.

  • Ex. A 6V battery will supply more current than a 1.5 V battery.

Voltage across the load is ______proportional to current.

  • Ex. The 6 V bulb will slow down current more than the 1.5 V bulb.

Resistance is ______proportional to current.

  • Ex. If a 1.5 V battery is connected to a circuit with high resistance, less current will flow compared to if the same battery was connected to a circuit with lower resistance.

OHM’S LAW

By measuring the amount of current that a given voltage produces, German physicist Georg Ohm was able to calculate a circuit’s resistance.

  • electrical resistance: ______
  • unit = ______(___)
  • measured using a device called an ______
  • Ohm’s Law: the mathematical relationship comparing______(V), ______(I), and ______(R).

SAMPLE PROBLEMS

  1. An electrical motor has an operating resistance of 25 Ω when a 4.8 A current is flowing through it. What is the potential difference of the outlet that the motor is plugged into?
  1. A car headlight has an average resistance of 24 Ω. Car batteries provide a potential difference of 12 V. What amount of current passes through the headlight?
  1. A 9.0 V battery maintains a current of 3.0 A through a portable radio. What is the resistance of the conductor?

Converting prefixes

  • milli (m) represents ______
  • Ex. 200 mA =
  • kilo (k) represents ______
  • Ex. 2.5 kΩ =
  • mega (M) represents ______
  • Ex. 15 MV =

MORE SAMPLE PROBLEMS

  1. The current through a load in a circuit is 120 mA. If the potential difference across the load (bulb) is 6 V, what is the resistance of the load?
  1. A 12 kΩ load is connected to a 90 V power supply. What is the current through the load in milliamperes (mA)?

DETERMINING RESISTANCE

Method 1: Use Ohm’s Law

Method 2: Use an ohmmeter

RESISTORS

  • resistor: ______

______

  • Controls current or voltage to provide the right amount for other components of the circuit.
  • energy not really “lost” it is ______
  • circuit symbol:

RESISTOR COLOUR CODE

  • A band of colour that have a corresponding numerical value that indicates the resistance of the resistor.
  • Refer to Table 8.2 on p. 297

The four bands of the colour code represent the following:

1st band = the first digit of the resistance

  • Ex. brown =

2nd band = the second digit of the resistance

  • Ex. orange =

3rd band = the multiplier or power of 10

  • Ex. red =

4th band = the percentage of accuracy

(gold = 5%, silver 10%, and no colour =20%)

  • Ex. gold =
  • The resistance of the above resistor is: ______or ______and is accurate within _____%.

SUMMARY: