Download Review – Electricity Unit

Review – Electricity Unit
Name: Answer Key
1. Fill in the blanks to explain the laws of attraction and repulsion using the words “attract”, “repel”
or “do not attract or repel”
a) Objects with the same charges _______repel_______________________________
b) Objects with opposite charges ________attract______________________________
c) Neutral objects _______do nothing________________________________________
d) A charged object and a neutral object will ____attract_________________________
2. Use the electrostatic series below to answer the following questions:
(Weak hold on electrons)
Acetate
Glass
Wool
Fur
Silk
Aluminum
Cotton
Ebonite
Gold
(Strong hold on electrons)
a) If ebonite is rubbed with fur, which one will be
positively charged?
__fur______________________________
b) If acetate is rubbed with silk, which one will be
negatively charged?
__silk______________________________
c) If cotton is rubbed with aluminum, which one will
lose electrons?
__aluminum__________________________
d) If gold is rubbed against a wool sweater, which one will gain electrons?
____gold________________________________
e) Gold and silk are rubbed together and charged. After they are charged, they are held near
each other, but not touching. Which of the following would likely be observed?
i. Gold and silk would attract and move towards each other
ii. Gold and silk would repel and move away from each other
iii. Gold and silk would not attract or repel (no movement at all)
3. What are the two ways of charging?
Friction and contact
4. Charging by __friction___________________ produces ___opposite___________ charges.
Charging by __contact___________________ produces ___same______________ charges.
5. A positive object comes into contact with a neutral object. Draw 2 diagrams showing before and
after they touch.
See overhead in class (both objects should be positively charged) – remember only the electrons
move
6. Describe the function of the four parts of a circuit listed in the table below:
Part
Energy Source
Load
Provides energy to the electrons
Converts electrical energy into useful energy
Conducting Wire
Control Device
Function
Path for the electrons to travel
Controls the circuit and it’s components (on or off)
7. Fill in the following table to describe current, voltage, and resistance.
Definition
Symbol
Unit
Current
The rate at which electrons flow through a
circuit.
I
Ampere (A)
Voltage
The electrical force or pressure that causes
current to flow (energy of the electron)
V
Volts (V)
Resistance
The ability to slow down or stop electrical flow
R
Ohm ()
8. Draw a circuit diagram with a 3 cell battery, a closed switch, and 2 motors in series. Also add an
ammeter to your diagram to measure the current in the circuit.
9. Draw a circuit diagram with a 2 cell battery, a motor, and a light bulb in parallel. Add an open
switch so that the light bulb is turned off but the motor still works.
Draw a voltmeter across the battery to measure the voltage output.
10. How are resistance, voltage, and current related? Hint: Draw your triangle and all equations.
Ohm’s Law
V=IxR
R=V/I
I=V/R
11. Emily is making a milkshake with a blender. The blender uses 120 V and has a resistance of
300 . How much electric current is flowing through the blender?
V= 120 V
I=?
R= 300 
I=V/R = 120V/300=0.4 A
Therefore there is 0.4A of electric current flowing through the blender.
12. Determine the percent efficiency of a radio that uses 30 000 J of electrical energy to produce
5000 J of sound energy.
% Efficiency =(output/input)x100
= (5000J/30 000J) x100
= 16.7%
Therefore the percent efficiency of the radio is 16.7%.
13. What are the 2 main components involved in producing electricity?
Turbine and generator
14. What is the difference between renewable and nonrenewable energy resources?
Renewable energy resources can be generated over and over again without being used up and
nonrenewable can not be regenerated in a short period of time.
15. Fill in the following table.
Method of Electrical Production
Hydroelectric
What turns the turbine?
water
Renewable or Nonrenewable?
renewable
Nuclear
steam
nonrenewable
Fossil Fuel
steam
nonrenewable
Wind
wind
renewable
Biomass
steam
renewable
16. What are two safety precautions you can take at home when working with electrical equipment?
Turn off the main breaker when working with electrical outlets, no electric appliances in the
shower or bath tub, no metal objects into the toaster, etc.