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This unit is a review of Grade 9 Electricity. Feel free to use your old notes.
Day 1; Electric Charge & Electric Fields
Day 1; Electric Charge & Electric Fields
Objects can be charged by adding or removing electrons from an object. If an object has a surplus of electrons it is negative, if it has a deficit of electrons it is positive.
Objects can be charged by Friction, Induction, Contact (or Conduction). A charge can also be removed by use of Grounding.
The total charge of an object (q) is directly proportional to the number of electrons (N) that have been transferred.
Therefore:
q = Ne
Where e is the fundamental/elementary charge: 1.60 x10-19C (positive for a proton and negative for an electron). Charge is measured in Coulombs (C).
Electric Fields are defined by drawing the path an imaginary, mobile, positive test charge would follow if placed near the charged object.
(Source)
(Source)
Complete Electrostatic Problems you will need the Electrostatic Series
Day 2; Current & Voltage
Day 2; Current & Voltage
Current
Current
Current is a measure of the flow of electrons. Imagine standing at a point on a wire and counting how much charge passes by you every second.
Units: Amperes (or Amps)
Measured with: Ammeter.
I = q/t
Where I = Current (Amps, A)
q = charge (Coulombs, C)
t = time interval (seconds, s)
Complete Current Problems
Voltage
Voltage
Voltage, or potential difference, is a measure of the energy given to or given up by the electrons.
Units: Volts
Measured with: Voltmeter
V = E/q
Where V = Voltage (Volts, V)
E = Energy (Joules, J)
q = Charge (Coulombs, C)
Complete Voltage Problems
Day 3; Circuits
Day 3; Circuits
All circuits consist of:
A source: this provides the electrons with the energy required to power a device. Example; a battery.
A load: this uses the energy carried by the electrons. Example; a light bulb.
Conductors: This provides the electrons with a pathway between each component. Example; a wire.
A fourth, optional, component is usually included:
A control: this allows the flow of electrons to be stopped. Example; a switch
An electrical circuit must make a loop from the battery through the other components and end back at the battery.
Electrical symbols are used to make diagrams easier to read and communication easier.
Series circuits
A series circuit is a circuit where the electrons only have one path to take between multiple loads.
Parallel Circuits
A parallel circuit is a circuit where the electrons can take multiple pathways, passing through a different load along each pathway.
Combination Circuits
A circuit consisting of series and parallel parts.
To measure current:
The multi-meter must be set up as an Ammeter. One wire must be in COM, one must be in 10A. Turn the dial to 10A. To measure the current, the meter must be placed in series with the device that you wish to know the current of.
To measure voltage:
The multi-meter must be set up as a Voltmeter. One wire must be in COM, one must be in V. Turn the dial to 20V. To measure the voltage the meter must be placed in parallel with the device that you wish to know the voltage of.
Activity: Build circuits, use ammeter and voltmeter.
Resources: PhET Circuit Builder
Day 4: Kirchoffs Law Lab
Day 4: Kirchoffs Law Lab
Complete the lab given out in class
Day 5: Kirchoffs Law Problems
Day 5: Kirchoffs Law Problems
Using Kirchoffs Laws, complete Kirchoffs Law Problems
Day 6: Ohms Law Lab
Day 6: Ohms Law Lab
Complete the lab given out in class
Day 7: Resistance
Day 7: Resistance
Ohms Law
Ohms Law
Resistance is a physical property of an object. It is a measure of how much an object opposes the electron flow and is calculated using Ohms Law:
R = V/I
Where: R = Resistance (Ohms, Ω )
V = Voltage (Volts, V)
I = Current (Amps, A)
Resistance of a Wire
Resistance of a Wire
Different factors affect the resistance of a wire:
Length: the longer a wire is the greater the resistance. R∝L.
Cross-sectional area: The thicker the wire, the less the resistance. R∝1/A. But A∝r2 and so R∝1/r2.
Type of material: Some materials conduct electrons better than others and so have a lower resistance. This is known as the resistivity (ρ) of a material (units Ωm). R∝ρ.
Temperature: When an object is heated the molecules vibrate more, impeding the flow of electrons more, therefore increasing resistance. However this is not true for all substances.
Resistance in Circuits
Resistance in Circuits
The resistance in a circuit can also be calculated.
If the current and voltage of a component is known then the resistance of the component can be calculated using Ohms Law.
If the current and voltage at the source is known then the total resistance of the circuit can be calculated using Ohms Law.
Resistance in Series:
If an electron passes through two resistors it experiences a resistance from both, and so the total resistance of is: RT = R1 + R2 + R3 + .... Rn (where n is the total number of resistors)
Resistors in Parallel:
If an electron can take one of multiple paths then they will take the path of least resistance. This means that each electron experiences the resistance of the weakest resistor. However, if all the electrons take that path, then that wire will become more negative than the other pathways and so some electrons will take the next path of least resistance. Although these electrons will have experienced a greater resistance than the first electrons as a whole, all of the electrons get through the circuit a bit faster than they would if they had all taken one path. This means that the total resistance of the circuit is actually lower than that of the lowest resistor. To calculate total resistance for a parallel circuit: 1/RT = 1/R1 + 1/R2 + 1/R3 + .... 1/Rn
Complete Resistance Problems.
Day 8: Complete Circuit Analysis
Day 8: Complete Circuit Analysis
Using Kirchoffs Laws and Resistance find all the unknowns in these circuit diagrams.
Day 9: Power & Cost
Day 9: Power & Cost
Power
Power
Power is the rate at which energy is transferred or transformed.
P = E/t
Where P = Power (Watts, W)
E = Energy (Joules, J)
t = time (seconds, s)
However from Voltage & Current, we know:
E = VQ and Q = It
Therefore;
P = VQ/t
and
P = VI
Cost of Electricity
Cost of Electricity
When we buy electricity, we pay for the amount of energy that we use. As 1 J is a very small amount of energy and we would use billions of Joules each month a new unit was derived:
Power is measured in KW
Time is measured in h
E = Pt
Therefore Energy is measured in KWh. We pay for every KWh we consume.
Complete Power Problems.
Complete Cost Problems.
Day 10: Review
Day 10: Review
Day 11: Unit Test
Day 11: Unit Test
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