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Electricity Review Assignment
1. Explain the meaning of the word “STATIC”. Now, explain what static electricity is.
The word static means still. Static electricity involves the build up of electrons on the surface of an
insulating material. The electrons remain “still” until they are discharged by coming near another
object. Static electricity is the IMBALANCE of electrons between 2 objects.
2. What is the difference between a positive charge and a negative charge?
An object has a negative charge if it has gained extra electrons and now has more electrons than
protons.
An object will have a positive charge if the object has lost electrons. There will now be more prtotons
than electrons so the object has a positive charge.
3. What are the 3 laws of electrostatics?
Negative and Negative charges will repel
Positive and Positive charges will repel
A negative and a positive charge will attract
4. Explain the difference between a conductor and an insulator.
An insulator is a material that holds its electrons very tightly and therefore will not let additional
electrons pass through it easily.
A conductor is a material that has loose electrons and when additional electrons are forced into the
material, they can pass the electrons through the material with very little resistence.
5. List the 4 basic components of an electrical circuit system.
Component
Description
__SOURCE____
A source is where the electrical energy comes from
or where it is generated
battery, plug-in
__LOAD______
A load is the object that converts the electrical energy
into some other form of energy
A conductor is the material that allows the electricity to
move around the path or circuit
A control will allow or disallow the flow of the current
light, stove element
__CONDUCTOR_
_CONTROL_______
Examples
copper wire
switch
6.
Wire
Resistor
Cell
Variable resistor
Lamp (2 ways)
7. What are an ammeter, a galvanometer and voltmeter? Explain what they measure and the units that
they measure in.
These are devices that measure electrical values.
Ammeter – measures current in Amperes (A)
Galvanometer – also measures current (but weaker current) in Amperes or small versions (ex. mA)
Voltmeter – measures voltage. The unit for voltage is volts (V)
8. What is resistance? Explain the idea of resistance using a diagram to illustrate what you understand
about this concept.
Resistance is provided by objects that impede the flow of electrons. Good diagram examples could be
like a bottle neck of traffic or the pinching off of a hose.
9. Explain how a toaster works, according to the idea of resistance.
A toaster receives a supply of electrons traveling from the power source through its power cord
(conductor). The heating elements in the toaster act as a resistor and when the electrons reach it, the
material resists their flow. Some of the electrons undergo an energy transformation, converting to heat
and light. The heat cooks your toast.
10. What is a variable resistor? Provide two examples.
A variable resistor is a resistor in which the user can control how much current is being resisted. If there
is very little resistance, the object will not release as many electrons as (heat, light, sound, motion, etc..).
If there is lots of resistance, the object will need to release more electrons in one of the above forms.
Examples – dimmer switch, dial on a toaster that determines how dark your toast gets, the volume knob
of a stereo, etc…
11. According to Georg Ohm, what is the relationship between current, voltage and resistance? How
can it be calculated?
There is a direct relationship between voltage and current. If one goes up, so does the other.
There is an inversely proportional relationship between current and resistance. If one goes up, the
other one must go down.
The Formula for Ohm’s Law is V=I x R
12. Explain how an electric cell works. What 2 components help make up an electrical cell?
An electric cell has 2 main parts – 2 different metals (electrodes) and a conducting liquid/paste
(electrolyte) It will convert chemical energy into electrical energy.
When the circuit is connect, IONS form from the electrodes and take part in chemical reactions with the
electrolyte. One of the electrodes will tend to lose electrons and the other will gain electrons. The
electrons will travel through the circuit and power the load (device) in the circuit.
13. According to our lab work, did the types of metals or the type of solution affect the amount of
voltage generated in our wet cells more? What solutions worked the best and what metals worked the
best?
The type of metals had a bigger impact than the type of liquid.
14. What is the difference between AC and DC electricity?
DC means direct current. It will travel one direction. This is the type you have in a battery
AC means alternating current. The current will travel both ways (a certain number of times per second).
This is what the wall socket (household power) uses.
15. What are fuses and what are circuit breakers?
Fuses and Circuit Breakers are safety devices that prevent too much current from flowing into the
electronic device.
A fuse has a type of metal that acts a resistor. If the metal receives too much current, it will melt and
interrupt the circuit (similar to a switch)
A circuit breaker is the same idea as a fuse, except it uses metals that will expand when there is too
much current. It will then trigger a spring which will flip the breaker so there is no longer a connected
current.
16. Calculations - Using Ohm’s Law, find the missing value
a) A circuit has a load that resists the flow of current by 12 ohms. The amount of current is 4
Amperes. What is the voltage through the circuit?
V= ?
I=4A
R = 12 ohms
V= I x R
V = 4 x 12
V = 48 Volts
b) A circuit is powered from a 240V plug in. If there is a 3 A current, what was the resistance of the
load?
V = 240V
I=3A
R=?
V = IxR
240 = 3 x R
divide by 3
80 = R
R = 80 ohms
or
R= I
V
R = 240
3
R = 80 ohms
c) A car has a 12V battery. If the current is 15 A going to the starter, what is the resistance?
V = 12 V
I = 15 A
R=?
V=IxR
12= 15xR
divide by 15
0.8 = R
or
R = 0.8 ohms
17. List the top 3 sources of electrical energy in Saskatchewan. (text page 278)
# 1 coal = 46%
#2 gas = 25%
#3 hydro = 23%
R= I
V
R = 12
15
R = 0.8 ohms
18. Describe how either a hydroelectric dam works….or …. Describe how a coal based electrical
generating station works.
Hydroelectric – A Hydroelectric power station uses the movement of water to generate power. The
water is held back by a dam. The water is forced to flow through the penstock which makes it pass by a
turbine which the water turns. The spinning of the turbine will allow the generator to convert the
mechanical (movement) energy into electricity. (Electrical energy)
A coal generating station works in much the same way, except it is the pressure of steam that turns the
turbine. Crushed coal is burns to heat water. The water will turn into high pressure steam which will
travel through pipes to turn the turbine. The spinning of the turbine allows the generator to change the
mechanical energy into electrical energy.
Cost calculations will be on the website
This is the sheet that says Calculation review for exam. You have it already.