what we are doing today ? 1) hand in lab 40 (formal & informal) 2) if you missed the lab 40...
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What we are Doing Today ?
1) Hand in Lab 40 (formal & informal)
2) If you missed the lab 40 formal lab (ie. You were absent with a legit excuse, you will be doing lab 41/42 as a formal.
3) Make sure you finished the HW p.173 of the textbook questions 10-18
• Electrical Power: The amount of work an electrical device can perform per second.
Pe = W / Δt
Pe = The electrical Power in Watts (W)
W = The Work in Joules (J)
Δt = the time interval (in s)
• Question
What is the electrical power an ipod can perform in 2 minutes with 200 J of work?
What do we know?Pe = ?Δt = 2 min = 120 secW = 200 J
Pe = W/Δt
Pe = 200J / 120sec = 1.67 W
Answer: the electrical power is 1.67 W
We can also express electrical power as:
Pe = V x I
Pe = is the electrical power in Watts (W)
V = is the potential difference in Volts (in V)
I = is the current intensity in Amps (A)
• Question
What is the potential difference at an ipods terminals if the electrical power is 1000W and the current intensity is 50 Amps ?
What do we know?Pe = 1000 W I = 50 A V = ?
Pe = V x I V = Pe / I
V = 1000W / 50 A = 20 V
Answer: the potential difference is 20 V
We can also express the formula for the relationship between electrical power and electrical energy
E = Pe x Δt
E = the electrical energy used (in Joules or kWh, kilowatt hours)
Pe = is the electrical power in Watts (W)
Δt = the time interval in seconds or hours
1 kWh = 3 600 000 Joules
• Question
What is the amount of energy a 10 000 W car (driven by Mr. Garrety) use in 12 minutes?
What is the amount of energy a 10 000 W volkswagon beetle (driven by Mr. Garrety) use in 12 minutes?
What do we know?Pe = 10000 W Δt = 12min x 60sec = 720 seconds E = ?
E = Pe x Δt
E = 10000 W x 720 seconds = 7200000 J or 2 kWh
Remember
1 kWh = 3 600 000 Joules
EST (Chapter 5)
• Coulomb`s Law: It explains how strong the force will be between two electrostatic charges. Electrostatic means electric charges without any motion.
F = the electrical force in Newtons (N)K = Coulomb’s constant, which is 9 x 109 Nm2/C2
q1 = the charge of the first particle (in C)q2 = the charge of the second particle (in C)r = the distance between the 2 particles (in metres)
Question
What is the electrical force between two positively charged particles that are placed 5 cm apart and that each have a charge of 5 x 10-8 C ?
What do we know?k = 9 x 109 Nm2/C2
q1 = 5 x 10-8 C
q2 = 5 x 10-8 C
r = 5 cm = 0.05 m
F = ?
F = 9 x 109 Nm2/C2 x 5 x 10-8 C x 5 x 10-8 C / (0.05m)2
F = 9 x 10-3 N or 0.009 N
measuring current
Electric current is measured in amps (A)
using an ammeter connected in series in
the circuit.
A
measuring current
A A
This is how we draw an ammeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
measuring voltage
The ‘electrical push’ which the cell gives to the
current is called the voltage. It is measured in
volts (V) on a voltmeter
V
measuring voltage
V
This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
V