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Warmup
100,000 J of energy are added to a 10g block of ice starting at -5*C. What
temperature does it end up at?
Q = m C ∆T
Q=mL
Cs = 2.11 J/g K
Cl = 4.18 J/g K
Cg = 2.08 J/g K
Lf = 334 J/g
Lv = 2260 J/g
MARCH 30TH, 2012
Electromagnetism Basics
Essential Standard
Students can solve problems to determine characteristics of circuits involving voltage
sources, resistors, and capacitors using Ohm’s Law and the Power Law. Students can
draw and interpret field diagrams and relate them to the force on a charged particle.
Students understand how a transistor operates and how it is used in technology.
Students understand the link between electricity and magnetism and can identify the
orientation of a current or magnetic field using the Right Hand Rule.
Vocabulary
Concept
Variable
Unit Label
Definition
Voltage
V
Volts (V)
How hard the electrical field is
pushing electrons
Current
I
Amps (A)
(coloumbs/s)
How many electrons flow per
second
Resistance
R
Ohms (Ω)
How easily the material allows
the electrons to move
Power
P
Watts (W)
(coloumbs * volts/ s)
Work done per second
Charge
q
Coloumbs (C)
6.24×1018 electrons or protons
Inductance
L
Henries (H)
How much a current affects (and
stores potential energy) in
magnetic fields
Capacitance
C
Farads (F)
(coloumbs/volt)
How much charge can be built
up as a result of a voltage
Circuit Diagram Symbols
Voltage Source
Wire
Meter
Resistor
Capacitor
Inductor
Switch (closed)
Switch (open)
Ground
Practice Diagrams
Equations
V=I*R
P=I*V
xt = x 1 + x 2 + x 3 …
1/xt = 1/x1 + 1/x2 + 1/x3…
Ohm’s Law
Power Law
Serial resistors or parallel capacitors
Parallel resistors or serial capacitors
Practice Problems
(Ohm’s and Power Laws)
If the voltage in the system is
increased:
I) The force on electrons is increased.
II) More current should flow.
III) More power will be consumed.
1.
2.
3.
4.
5.
6.
I and II
I, II, and III
I and III
II and III
III only
None of the above
60%
20%
10%
1
2
3
10%
0%
0%
4
5
6
Batteries store:
1.
2.
3.
4.
5.
6.
Charge
Current
Voltage
Inductance
Capacitance
Power
25%
17%
17%
17%
17%
8%
1
2
3
4
5
6
If you lower the voltage on a charged
capacitor:
1. Current will flow forward
to increase the charge.
2. The power of the system
decreases.
3. Current will flow
backwards to decrease the
charge.
4. Inductance will store lost
energy in a magnetic field.
5. None of the above.
67%
25%
8%
1
2
3
0%
0%
4
5
A circuit has a resistance of 4 Ohms and a voltage of 3
Volts. What current flows through it?
1.
2.
3.
4.
5.
6.
7.
8.
4/3 Amps
¾ Amps
1 Amp
12 Amps
4/3 Farads
¾ Farads
1 Farad
12 Farads
57%
21%
14%
7%
1
2
3
0%
0%
0%
0%
4
5
6
7
8