Download Physical Science Chapter 6 (Electricity) Notes

Physical Science Chapter 6 (Electricity)
Notes
SECTION 1 (Electric Charge)
1) An atom naturally has no electrical charge; that is, it is electrically neutral. When an atom gains or loses an electron it then
acquires a charge and is ionized.
a) To be electrically neutral an atom must have the same number of protons and electrons.
i) A proton has a positive charge.
ii) An electron has a negative charge.
b) An electric charge can be transferred from object to another- (movement by the electron).
c) In an atom the electron (which has a negative charge) is the only particle that can move.
d) When an atom gains an electron it becomes negatively charged because the electron carries a negative charge.
e) When an atom loses an electron it becomes positively charged for the same reason.
f) Atoms with like charges repel each other, and atoms with opposite charges attract each other.
2) Static electricity – the accumulation of excess electric charge on an object.
3) Law of Conservation of Charge – an electric charge cannot be created or destroyed. The charge, in the form of an electron
can be moved from one place to another.
4) Electric Discharge (ESD) – the transfer of an electric charge. When two oppositely charged objects come in contact,
electrons will move until both objects are electrically neutral.
5) Electric Field—surrounds every electric charge and exerts the force that causes the other electric charge to be attracted or
repelled.
6) Conductor—is a material that has little resistance to electron flow. Examples are aluminum, copper, iron, and gold.
a) Skin Effect--since the flow of the charge is electrons and all electrons are negative the electrons tend to repel each other
and move to the outside of the conductor.
7) Insulator—is a material that has high resistance to electron flow. Examples are glass, rubber, and plastics.
8) Charging by contact—is the process of transferring charge by touching or rubbing.
9) Charging by induction—the rearrangement of electrons on a neutral object caused by a nearby charged object. Induction
uses the magnetic field created by the charge to induce electrons to move if they are within the magnetic field.
10) Electroscope—is a device that can detect electric charge.
SECTION 2 (Electric Current)
1) Electric Current – the flow of electrons from one place to another. The flow of electrons is also known as current with the
symbol of (I).
2) Voltage difference—is the push that causes charges to move and is measured in volts (V). The large the voltage the larger
the build up of electrons in one area and the lack of electrons in another area.
a) Voltage is also known as both a potential difference (potential energy) and as EMF (electro-motive force).
b) Electrical Potential Energy – the electrons stored energy. Better known as voltage.
3) Electric circuit—is a close path that electric current follows.
4) Electric cell – converts chemical energy into electric energy. The cell contains two terminals (positive and negative) of
different kinds of metals. The cell also contains an electrolyte. An electrolyte is a substance that allows an electric current to
be conducted. There are two types of cells: dry and wet.
a) Dry cell – the electrolyte is a paste.
b) Wet cell – the electrolyte is a liquid.
5) Battery – a collection of two or more electric cells.
6) Resistance-- is the tendency for material to oppose the flow of electrons, changing electrical energy into thermal energy and
light.
a) The unit for resistance is the ohm and is given by the Greek symbol omega (Ω).
7) Ohm’s Law – used to measure voltage, resistance, and current in a circuit.
V = IR
V = voltage
I =current
R = resistance
V
I
R
8) In an electric circuit the electrons flow from the negative pole to the positive pole. There are two types of currents: direct
current and alternating current.
i) Direct current (DC) – the electrons flow in only one direction.
ii) Alternating current (AC) – the electrons repeatedly change direction in their flow.
Physical Science Chapter 6 (Electricity)
Notes
9) Coulomb’s Law – used to determine the charge and voltage on a capacitor
C=
C = capacitance
Q = charge
V = voltage
Q
V
Q
C
V
SECTION 3 (More Complex Circuits)`
1) Electric circuit – the path electricity follows. There are two types of circuits, series and parallel
2) Series circuit – only has one path for the electricity to follow. The current flows from the negative pole to the positive pole.
+
3) Parallel circuit – has two or more separate paths through which electricity can flow. The current flows from the negative pole
to the positive pole.
+
4) Safety Devices—Fuse (Small piece of matal that melts if the current becomes too high) Circuit Breaker (bimetallic strip that
bends and switches the switch off if the current becomes too high)
5) Capacitor – consists of two metal plates separated by an insulator. Electric charge will build up on one plate until enough
charge has accumulated to “jump” the gap between the plates.
6) Open circuit – a circuit in which the switch is off or there is a break in the circuit.
7) Closed circuit – a circuit in which the switch is on or there are no breaks in the circuit
8) Power – the rate at which energy is delivered. Power is measured in watts.
P = IV
⇒
watts = ( amp )( volt )
2
P=I R
⇒
watt = ( amp ) ( ohm )
V 2
R
⇒
watt =
P=
⇒
⇒
2
( volt )
watt = IV
watt = I 2 Ω
2
⇒
ohm
watt =
V2
Ω
9) Kilowatt-hour—is the unit of electrical energy. One-kilowatt hour is 1000 watts of power used in one hour.
Chapter 6 Equations
⎧ C = capacitance
Q ⎪
C=
⎨Q = charge
V ⎪
⎩ V=Voltage
P = IV
⎧V = voltage
⎪
⎨ I=current
⎪ R = resistance
⎩
V =IR
V2
R
SERIES CIRCUITS
P = I 2R
P=
PARALLEL CIRCUITS
POWER
Pt = P1 + P2 + P3 + ...Pn
Pt = P1 + P2 + P3 + ...Pn
CURRENT
I t = I1 = I 2 = I 3 = ...I n
I t = I1 + I 2 + I 3 + ...I n
VOLTAGE
Vt = V1 + V2 + V3 + ...Vn
Vt = V1 = V 2 = V 3 = ...VN
RESISTANCE
Rt = R1 + R2 + R3 + ...Rn
CAPACITANCE
1
C1
+
1
C2
1
+ C13 + C1n
1
R1
+
1
R2
1
+ R13 + R1n
C t = C1 + C 2 + C3 + ...C n