1. Topic 5.1 Electric potential difference, current and resistance
Electric Currents
Topic 5.1 Electric potential difference, current and resistance

2. Simple Circuit What does a simple circuit include?
Circuit implies a flow. What is flowing?
How do you know there’s a transfer of energy?
Can we see any of this?

3. Analogy

4. Advanced Analogy Energy Removed from the System
Energy Added to the System
Energy Removed from the System

5. Definitions What are charges?
How do we use charges to produce potential movement?
What happens when there is a charge in the middle?
The charges will have kinetic energy
energy changes when current flows.

6. Energy between metal plates
What needs to be done to move a negative charge from the red to blue plate?
What happens to the charge when it’s at the blue plate?
What happens when it’s released?
If you want to move a charge closer to a charged plate you have to push against the repulsive force
You do work and the charge gains electric potential energy.
electrical energy is PE and how Potential Difference is related to the energy of the charges.
If you let go of the charge it will move away from the plate, losing electric potential energy, but gaining kinetic energy.

7. Potential Difference
Energy needed to move a charge from A to B

8. ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺

9. cell
energy ☺
electron
lamp

10. Current What is current? How would we measure current?
Conventional Current
1 amp is a flow of about 6 x 1018 electrons in each second
Electron Flow

11. Resistance What is electrical resistance?
The greater the resistance of a component, the more difficult it is for charge to flow through it.

12. Ohm’s Law
The greater the resistance of a component, the more difficult it is for charge to flow through it.

13. Ohmic vs Non-Ohmic Resistors
ohmic means constant resistance, non-ohmic means the resistance is not constant

14. Back to the Electric Circuit
Where does the energy come from in an electric circuit?
Where does the energy go?
What determines the amount of energy that is ‘taken’?
What is carrying the energy?

15. Definitions Charge, Q Current, I Potential Difference, V (Voltage)
Resistance, R
If units of charge are
coulombs [C], derive
the units for I, V, and R
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

16. Definitions 1 coulomb = 6 x 1018 electrons of charge Current, I
Potential Difference, V (Voltage)
Resistance, R
If units of charge are
coulombs [C], derive
the units for I, V, and R
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

17. Definitions 1 coulomb = 6 x 1018 electrons of charge
Current = Charge / Time
Potential Difference, V (Voltage)
Resistance, R
If units of charge are
coulombs [C], derive
the units for I, V, and R
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

18. Definitions 1 coulomb = 6 x 1018 electrons of charge
Current = Charge / Time
Potential Difference = Energy / Charge
Resistance, R
If units of charge are
coulombs [C], derive
the units for I, V, and R
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

19. Definitions 1 coulomb = 6 x 1018 electrons of charge
Current = Charge / Time
Potential Difference = Energy / Charge
Resistance = Voltage / Current or
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

20. Units
𝐼= 𝑄 𝑡 = [𝐶] [𝑠] = 𝑎𝑚𝑝𝑒𝑟𝑒 = 𝐴 𝑉= 𝐸 𝑄 = [𝐽] [𝐶] = 𝑣𝑜𝑙𝑡 = 𝑉 𝑅= 𝑉 𝐼 = [𝑉] [𝐴] = 𝑜ℎ𝑚 =[Ω]
Coulombs are like a ‘bag of electrons’
Current = Q/t
PD = V = E/Q

21. The electron volt (eV)
One electron volt (1 eV) is defined as the energy acquired by an electron as a result of moving through a potential difference of one volt
1 eV = ? J
Since W = q x V
And the charge on an electron or proton is 1.6 x 10-19C
Then W = 1.6 x 10-19C x 1V
W = 1.6 x J
Therefore 1 eV = 1.6 x J

22. The electron volt (eV)
One electron volt (1 eV) is defined as the energy acquired by an electron as a result of moving through a potential difference of one volt
1 eV = 1.6 x J
Since W = q x V
And the charge on an electron or proton is 1.6 x 10-19C
Then W = 1.6 x 10-19C x 1V
W = 1.6 x J
Therefore 1 eV = 1.6 x J

23. Inside the wire

24. Wire = Resistor
What happens when the electrons collide with the atoms?
What happens to the atoms when the wire is at a higher temperature?
How does this affect the resistance of the wire?
Temperature goes up as KE is transferred

25. Power Dissipation 𝑃= 𝑉𝑄 𝑄 𝐼 =𝐼𝑉 𝑃= 𝑊 𝑡 = 𝐸 𝑡 𝑉=𝐼𝑅; 𝑃=𝐼 𝐼𝑅 = 𝐼 2 𝑅
𝑃= 𝑉𝑄 𝑄 𝐼 =𝐼𝑉
𝑉=𝐼𝑅;
𝑃=𝐼 𝐼𝑅 = 𝐼 2 𝑅
𝐼= 𝑉 𝑅 ;
𝑃= 𝑉 𝑅 𝑉= 𝑉 2 𝑅
𝑃= 𝑊 𝑡 = 𝐸 𝑡
𝑉= 𝐸 𝑄 ; 𝐸=𝑉𝑄
𝐼= 𝑄 𝑡 ; 𝑡= 𝑄 𝐼

26. In summary