resistance factors equation (ohm’s law) interpreting graphs circuits and resistance
TRANSCRIPT
Resistance• Factors• Equation (Ohm’s Law)• Interpreting graphs• Circuits and Resistance
Here’s the deal• electrons move through a conductor. • electrons can collide with the atoms of the
conductor. • This makes it more difficult for the current to
flow.
Like a marathon…
• The roughness, difficulty and width of the road, including the obstacles along the way are some resistances to their forward motion.
• Length of wire• As length increases, resistance increases
• Diameter of wire• As diameter increases, resistance decreases
• Temperature• As temperature increases, resistance increases
So, in a conducting material, what factors affect the flow
of electrons?
Resistance•Measure of how a material or object opposes the flow of current•Ratio of pd across resistor and current in the resistor
Energy and Power•V = energy per unit charge•I = charge per unit time•Energy = VIt
• Unit: Joules, J•Power = energy per unit time•Power = VI
• Unit : Watts, W
Ohm’s Law
Volt(s)
Ampere(s)
Ohm(s)
Experiment 1
• Gradient is constant• Gradient = I/V = constant value• Resistance = 1/Gradient = constant value• Fixed Resistance• Fixed Resistor
What does the graph mean?
Experiment 2
• Gradient is changing decreasing• Gradient = I/V = decreasing value• Resistance = 1/Gradient = increasing value• Increasing Resistance• Filament bulb increases in temperature
What does the graph mean?
Interpreting Graphs
• What is the resistance when V=1 and V=3?
Interpreting Graphs• What is the
resistance when V=2, 5 and 5.5 volts?
Series Circuit
Itotal = I1 = I2 = In
Vtotal = V1 + V2 + Vn
Rtotal = R1 + R2 + Rn
Parallel Circuit
Itotal = I1 + I2 + In
Vtotal = V1 = V2 = Vn
= + +RnR2R1
1 1 1
Rtotal
1
• Series• The total resistance increases• The total current decreases
• Parallel• The total resistance decreases• The total current increases
What happens to the current in the circuit when you add more resistors?
• Series• More bulbs divide energy between themselves• Brightness decreases
• Parallel• Voltage or energy across each bulb is the same• Brightness is unaffected
What happens to the brightness of the bulbs when more are added?
• Series• There is only one path for current • Since bulb is busted, there is an open in the circuit• Other bulbs don’t light
• Parallel• The path for each bulb is independent• Other bulbs are lit; only busted bulb is unlit
What happens to the other bulbs in the circuit when one of the bulbs is busted?