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Chapter 20: Electricity
Section 20.1: Electric Charge and Static Electricity
1. Explain the concept of Electric Charge. It is a property of electricity that causes
subatomic particles such as protons and electrons to attract or repel one another.
2. Explain the concept of Electric Forces. Force used for attraction and repulsion
3. What is an Electric Field? This is an imaginary field that is emitted by a charged
subatomic particle.
4. What is Static Electricity? It simply refers to the net accumulation of electric
charges often times due to the transfer of electron. Can often cause shock.
5. Explain three ways discussed in the text that can help charge objects.
 Friction-When you rub items together, electric charges are transferred.
A good example of this is rubbing a balloon against your hair. The
electrons in your hair are transferred to the balloon thus leaving a net
negative charge in the hair. Because opposites attract you may notice that
your hair follows the balloon. See Example A on p602
 Contact: a good way to understand this concept is by looking at Fig B on
p602. When the young girl touches the charged generator. The electrons
are transferred to the girls hair. Because there are like charges, her hair
starts repelling one another.
 Induction- To understand this concept, suppose you’re walking across
the carpet. You start to pickup electrons from the carpet. When you
reach out to touch the door, before you touch it, the electrons orient
themselves in the opposite position of the electrons. If the charges don’t
repel you may feel the shock due to the charges being forced together.
Section 20.2: Electric Current and Ohm’s Law
1. Explain the two types of electric current.
Note: We describe current in the way that protons typically flow.
 AC-Alternating Currents- reverses during time.
 DC-Direct Currents- travels in one direction during time
2. Explain the difference between electrical conductors and electrical insulators.
 Electrical conductor- material that allows electric current to flow freely
 Electrical Insulators- materials that keep electric charges isolated to a
certain area.
3. What is the SI Unit for Electric Current? Ohms
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4. What effect can resistance have on electric current? Resistance can predict the
electric flow. The higher the resistance the harder it is for electrons to flow. The
less resistance the easier the flow.
5. What is a superconductor? A material that has almost zero resistance when
cooled to low temperatures.
6. Explain the concept Voltage. This is also known as Potential Difference. The
difference in electrical potential energy (stored energy) between two places in
an electric field.
7. Explain Ohm’s Law and know the formula for Ohms Law. A mathematical
relationship between voltage, current and resistance.
The formula: V=I x R or I = V/R
Section 20.3 Electric Circuits
1. Explain Circuit Diagrams- it’s a diagram where symbols represent parts of a
circuit.
2. Know the difference between open and closed circuits.
 Let’s say you have a circuit where all parts need to be connected in order
for the circuit to work. If we change a switch to where it’s not connected
in the circuit, it is then labeled as opened.
 A closed circuit is when all parts are connected and the electric current
can flow.
3. Know the difference between Series and Parallel Circuits
 Series Circuits operate similar to an open circuit. The electric current
flows in one direction only. This is similar to Christmas lights. When one
light is out they all are out.
 Parallel Circuits- There is two paths that the circuit can flow. In
comparison to the above illustration, if one bulb goes out, then the other
bulbs would still work.
4. Know the formula for Electric Power P(Watts) = I (amps) x V (volts)
5. Know the formula for Electrical Energy E= Px t
6. Be able to explain the difference modes of electrical safety indicated by the text.
 Home Safety. In older homes they used fuses where the center (resistor)
would melt if the circuit got to hot. In modern homes, we use a circuit
breaker where the switch opens to stop current ( in an open circuit) both
options help to prevent fires from starting.

Personal Safety- Never tough exposed wires. Also make sure that your
home’s electrical wiring is properly grounded. In this case, the electric
current is sent to the ground and not to you.
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Section 20.4 Electronic Devices
1. What is an electronic signal? Information sent as patterns in the controlled flow of
electrons through a circuit.
2. Know the difference between analog and digital signals
3. What is a Cathode- Ray tube (CRT)? It is a type of vacuum that can alter the type
current. The most common CRT’s are used in computer monitors.
4. What is a semiconductor? A crystalline substance that conducts electric current only
under certain conditions.
5. What is a transistor? A semiconductor that amplifies or strengthens an electrical
signal or acts as a tiny on-off switch.
6. What is an integrated circuit? This is a semiconductor that contains multiple
resistors, diodes, and transistors. A good example of an integrated circuit is a small
computer chip. When you look at the chip you notice you see several patterns etc. All of
those different patterns are different types of circuits.