1. Static & dynamic electricty ohm's law

2. Static Electricity
Static electricity describes all the phenomena related to electrical charges at rest.

3. How to charge an object?
An object can be charged in three different ways:
by friction
by conduction
by induction

4. Charging by Friction
Friction pulls electrons away from one of the objects and transfers them to the other.
Before: Two neutral objects
After: Two objects with opposite charges

5. Charging by Friction

6. Charging by Conduction
The charge of one object is shared between two objects when they come into contact.
Before: One charged object and one neutral object
After: Two objects with like charges

7. Charging by Conduction

8. Charging by Induction
The proximity of the charged object causes the charges in the neutral object to separate.
Before: One charged object and one neutral object
After: One charged object and one object carrying a partial positive charge on one side and a partial negative charge on the other side

9. Charging by Induction

10. Practice Problem
The five spheres below, identified A to E, carry an electrical charge. If sphere A carries a positive charge, what is the sign of the charges on each of the other spheres? + + + - + - - -

11. Electroscope
A simple electroscope consists of a glass jar in which two strips of gold leaf are suspended from a metal rod that conducts electricity.
The rod, which enters the jar through a stopper made of a material that does not conduct electricity, has a metal knob on the end outside the jar.

12. Electroscope

13. Electroscope
The strips of gold leaf hang straight down when they are not charged. When a charged body is brought near the metal knob, both strips acquire a like charge (that is, they both become negative or both become positive). As a result, they repel each other and spread apart to form an inverted V. The electroscope is then charged.
If an oppositely charged body is brought close to the knob, the charge on the strips is neutralized, and they again hang straight down. The electroscope is discharged.

14. Electroscope

15. Dynamic Electricity
Dynamic electricity describes all the phenomena related to electrical charges in motion.
Electric current is the orderly flow of negative charges carried by electrons.

16. Ohm’s Law
Ohm’s law states that, for a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity.

17. Ohm’s Law – Resistance
Resistance: The ability of a material to hinder the flow of electric current.
Symbol: R
Unit of measurement: Ohm (Ω)

18. Ohm’s Law – Potential Difference
Potential difference: The amount of energy transferred between two points in an electrical circuit.
Symbol: V
Unit of measurement: Volt (V)

19. Ohm’s Law – Current Intensity
Current intensity: The number of charges that flow past a given point in an electrical circuit every second.
Symbol: I
Unit of measurement: Ampere (A)

20. Ohm’s Law

22. Practice Problem #1
If the current in the circuit is 10 amps and the resistance is 3.0 ohms, what is the voltage?
STEP 1:
STEP 2:
STEP 3:
I = 10 A
R = 3.0 Ω
V = ?
V = IR
V = IR
V = (10 A) x (3.0 Ω)
V = 30.0 V
STEP 4:
The voltage of the circuit is 30.0 Volts.

23. Practice Problem #2
A current of 3.7 amps is running through a circuit with a resistance of 1.5 ohms. What is the voltage?
STEP 1:
STEP 2:
STEP 3:
I = 3.7 A
R = 1.5 Ω
V = ?
V = IR
V = IR
V = (3.7 A) x (1.5 Ω)
V = 5.55 V
STEP 4:
The voltage of the circuit is 5.55 Volts.

24. Practice Problem #3
If the battery in the circuit is 24 V and the resistance is 12 ohms, what is the current, I?
STEP 1:
STEP 2:
STEP 3:
I = ?
R = 12 Ω
V = 24 V
I = V/R
I = V/R
I = (24 V) / (12 Ω)
I = 2 A
STEP 4:
The current of the circuit is 2 Amperes.

25. Practice Problem #4
Given a voltage of 120 volts and a current of 5 amps, what is the resistance?
STEP 1:
STEP 2:
STEP 3:
I = 57 A
R = ?
V = 120 V
R = V/I
R = V/I
R = (120 V) / (57 A)
R = 2.11 Ω
STEP 4:
The resistance of the circuit is 2.11 Ohms.

26. Calculating Current Intensity
Current intensity can be determined using the following formula:
I is current intensity [A]
q is charge [C]
Δt is time [s]
I = q Δt

27. Calculating Current Intensityq I Δt

28. Practice Problem #5
The data sheet for a car headlight indicates that the light requires a current intensity of 15 A. What is the charge needed for one minute of operation?
I = 15 A
Δt = 60 s
q = ?
q = I Δt
q = I Δt
q =(15 A)(60 s)
q = 900 C
ANS: It takes a charge of 900 C to make the headlight work for one minute.

29. Calculating Potential Difference
Potential Difference can be determined using the following formula:
V is potential difference [V]
E is energy transferred [J]
q is charge [C]
V = E q

30. Calculating Potential Differenceq V

31. Practice Problem #6
The electrical circuits in our homes usually supply a potential difference of 120 V. What is the amount of energy transferred by a charge of 200 C?
V = 120 V
E = ?
q = 200 C
E = V q
E = V q
E = (120 V)(200 C)
E = J
ANS: A 200 C charge can transfer J of energy.

32. Ohm’s Law

33. Electrical Power
Electrical power (Pe) is the amount of work an electrical device can perform per second.
Unit of measurement: watt
Symbol: W

34. Pe = V I Electrical Power Pe is electrical power [W]
V is potential difference [V]
I is current intensity [A]

35. Calculating Electrical PowerPe V I

36. Practice Problem #7
Calculate the power rating of an i-Pod drawing 3.5 A from a 6.0 V battery.
Pe = ?
I = 3.5 A
V = 6.0 V
Pe = V I
Pe = (6.0 V)(3.5 A)
Pe = 21.0 W
Pe = V I
ANS: The i-Pod has a power rating of 21.0 Watts.

37. Electrical Energy
The amount of Electrical energy (E) used by an electrical device is found by multiplying its electrical power by time. This is a measure of the energy provided by electricity.
Unit of measurement: joule
Symbol: J

38. E = Pe Δt Electrical Energy E is electrical energy [J]
Pe is electrical power [W or kW]
Δt is time [s or hr]

39. Calculating Electrical EnergyPe Δt

40. Practice Problem #7
If a 1000-W microwave oven operates for six minutes, what is the amount of energy it uses?
Pe = 1000 W
Δt = 6 min = 360 s
E = ?
E = Pe Δt
E = Pe Δt
E = (1000 W)(360 s)
E = J
ANS: After six minutes of use, the microwave will consume J of energy.

41. Electrical Energy = WORK
HINT: If a problem asks you to find how much work is being done, simply calculate the elctrical energy.
Energy and Work can be treated as synonyms.
Unit of measurement: joule
Symbol: J

42. Practice Problem #8
How much work can a 1000 W car engine do in one minute?
Pe = 1000 W
Δt = 1 min = 60 s
W = ?
W = Pe Δt
W = Pe Δt
W = (1000 W)(60 s)
W = J
ANS: A car engine can do J of work in one minute.

43. Conversions 1 kW = 1000 W Ex: 3.6 kW x 1000 = 3600 W
Ex: 670 W ÷ 1000 = 0.67 kW
1 hr = 60 min = 3600 s
Ex: 3 hr x 60min/1hr = 180 min
180 min x 60sec/1min = sec

44. Work
Pe = W Δt
Pe is electrical power [W]
W is work [J]
Δt is time [s]

45. W Pe Δt Calculating Work
Work [J] and Electrical Energy [J] are interchangeable in the formula. W Pe Δt