MCAS Student Practice Questions UNIT 5 –Electromagnetism
Solutions
STANDARD 5.1
5.1. Recognize that an electric charge tends to be static on insulators and can move on and in conductors.
Explain that energy can produce a separation of charges.
11-14 5.1
Electric charges can move most easily on which of the
following objects?
A. glass tubes
B. metal plates
C. plastic cups
D. rubber tires
10-6 5.1 Which of the following conditions results in
the buildup of static charge on an object?
A. when neutrons outnumber electrons
B. when there are more protons than neutrons
C. when there are more electrons than
protons
D. when all neutrons have been removed from the
object
Standard: 5.1 - Recognize that an electric charge tends to
be static on insulators and can move on and in conductors.
Only electrons can be moved.
Explain that energy can produce a separation of charges.
10-35 5.1
9-18 5.1
A copper sphere, a glass sphere, a plastic sphere, and a A balloon is rubbed against a sweater. Which of the
rubber sphere are placed on individual insulating
following occurs because of the rubbing?
stands. A student touches each sphere with an
A. destruction of charged particles on the
electrically charged object.The sphere made of which
balloon
material will distribute the electric charge fastest over
B. release of charged particles from the air in
its entire surface area?
A. copper
B. glass
C. plastic
D. rubber
Standard: 5.1 - Recognize that an electric charge tends to
be static on insulators and can move on and in conductors.
Explain that energy can produce a separation of charges.
8-24 5.1
A teenager removes the plastic wrapping from a CD.
The pieces of wrap cling to her hand.
Which of the following forces causes the wrap to cling
to her hand?
the balloon
C. movement of negatively charged
particles from one material to the
other
D. movement of positively charged particles
from one material to the other
Only electrons can be moved.
7-20 5.1
Which of the following is least likely to result in the
generation of static charge?
A. peeling plastic wrap off a CD case
A. electrostatic
B. combing dry hair with a plastic comb
B. gravitational
C. rubbing one's shoes on a synthetic
carpet
C. magnetic
D. net
The force created by electrons being taken
by friction is called the Electrostatic Force.
D. drying one's body with a towel after
a shower
The water involved is the difference between this
situation and the others.
STANDARD 5.2
5.2. Develop qualitative and quantitative understandings of current, voltage, resistance, and the connection
between them (Ohm's law).
11-39 5.2 The measurements in the table are from four circuits that each
have the same components except for the battery. Which of the following
statements describes how voltage, current, and resistance are related by
Ohm’s law in these circuits?
A. As voltage increases, current decreases and resistance decreases.
B. As voltage increases, current increases and resistance stays
the same.
C. As voltage increases, current decreases and resistance stays the same.
D. As voltage increases, current stays the same and resistance decreases.
Follow the data of Voltage and Current in the chart and se that as the volatage increases so does the
current. The resistance = 3 through all examples.
11-42 5.2
The diagram below shows a simple circuit.
10-7 5.2
What is the voltage across the terminals of a
resistor that has 0.065 A of current flowing
through it?
A. 0.0028 V
What is the current in the circuit?
A. 0.83 A B. 1.2 A C. 2.0 A D. 22 A
B. 0.097 V
C. 1.5 V
D. 350 V
Ohm’s Law: V = IR
Ohm’s Law: V = IR
So I = V/R = (12 V ) /( 10 Ω) = 1.2 Amp
So V = IR = 0.065 A x 23 Ω = 1.495 Volts
10-33 5.2
A microwave oven uses 10 A of current when
connected to a wall outlet that provides 120 V of
electricity. What is the resistance of the microwave
oven?
A. 0.083 Ω
B. 12 Ω C. 110 Ω D. 1200 Ω
9-31 5.2
Large amounts of current can damage a circuit. Which
of the following changes in a series circuit will result
in an increase in current?
A. The voltage is halved and the resistance is
halved. (Result is same Current)
B. The voltage is halved and the resistance is
doubled. (Result is less Current)
Ohm’s Law: V = IR
C. The voltage is doubled and the resistance is
halved. (Result is more Current)
So R= V/I = (120 V ) /( 10 A) = 12 Ω
D. The voltage is doubled and the resistance is
doubled. (Result is same Current)
Current = I = V/ R to increase (I)current, increase V and
decrease R.
𝑽
𝑰=
𝑹
9-33 5.2
Based on Ohm’s law, which of the following
statements explains what must happen when the
voltage across a resistor is decreased?
A. The resistance of the resistor increases.
B. The resistance of the resistor decreases.
8-6 5.2
An ammeter measures the current
in the circuit shown here.
When the piece of wire labeled X is
replaced by a second identical R,
which of the following happens to
the current?
C. The current through the resistor increases.
A. It increases.
D. The current through the resistor
decreases.
B. It decreases.
When Voltage decreases, Current decreases as well.
C. It goes to zero.
D. It remains unchanged.
“replaced by a second identical R” means adding a
resistor in series which increases the resistance.
When resistance is increased the current must
decrease.
8-26 5.2
Which of the following ammeters is shown with an incorrect reading?
Determine the current in each case I = V/R
A
𝐼=
B
𝐼=
C
𝐼=
D
𝐼=
3𝑉
6𝛺
3𝑉
1𝛺
3𝑉
3𝛺
3𝑉
9𝛺
= .5𝐴
This matches the diagram
= 3𝐴
This matches the diagram
= 1𝐴
This matches the diagram
= .333𝐴
This does not match the diagram
7-3 5.2
A current of 2 A passes through two resistors placed in
series. The first resistor has a resistance of 10 and
the second resistor has a resistance of 20 .
What is the total potential difference across the two
resistors?
7-17 5.2
The graph below relates
the current to voltage
data for a resistor.
Which of the following is
the value of the resistor?
A. 13 V B. 15 V C. 30 V D. 60 V
A. 0.2 Ω B. 2 Ω
Series Resistors have the same current. So in this case
2 A.
C. 4 Ω D. 10 Ω
Determine the Voltage for each Resistor:
Use any point from the graph and calculate V / I
Ohm’s Law: V = IR
Examples:
8 V / .8 Amp = 10 Ω
So for 1st resistor: V = IR = 2 A x 10 Ω = 20 Volts
For 2nd resistor: V = IR = 2 A x 20 Ω = 40 Volts
4 V / .4 Amp = 10 Ω
Any point chosen will give the same result.
Adding the two together: =
20 Volts + 40 Volts = 60 Volts
7-21 5.2 The two resistors shown are connected to identical power sources.
Resistor 1 has a resistance of 30 , and resistor 2 has a resistance of 45 .
The current in resistor 1 is 2 A.
What is the current in resistor 2?
A. 1.0 A B. 1.3 A C. 1.5 A D. 3.0 A
“ identical power sources” means the voltage is the same for both. 1st
determine the voltage of the in the top example.
V = IR = 2 Amp x 30 Ω = 60 Volts
Use this as the voltage for the second example.
I = V/R = (60 Volts) / ( 45 Ω ) = 1.3333 Amps
STANDARD 5.3
5.3. Analyze simple arrangements of electrical components in both serial and parallel circuits. Recognize
symbols and understand the functions of common circuit elements (battery, connecting wire, switch, fuse, and
resistance) in a schematic diagram.
11-13 5.3
A circuit diagram is shown below.
11-34 5.3
The diagram below shows a
simple circuit.
Which component is the source
of energy in this circuit?
What is the current through the 2 Ω resistor?
A. 1.25 A B. 1.5 A C. 5.0 A D. 6.67 A
Voltage for parallel resistors is equal, in this case = 10
Volts. Ohms Law can be used.
D. The battery is the source of energy in the circuit.
I = V/R = 10 V / 2 Ω = 5 A
A is a switch, B is a resistor and C is a Fuse.
10-15 5.3
The diagram below shows a simple electric circuit.
9-39 5.3
A circuit diagram is shown below.
Which of the following statements describes the
function of the battery?
A. It reduces the flow of electrons.
B. It transmits light through the circuit.
C. It pushes electrons through the
circuit.
D. It releases light during a chemical reaction.
Which component in the diagram converts chemical
energy into electrical energy?
A. component W
B. component X
C. component Y
D. component Z
The battery is the source of energy or push for electrons.
The battery converts chemical energy into electricity.
8-15 5.3
In the diagram below, the circuit has one battery and two identical light bulbs.
If one light bulb is removed, which of the following could replace it so that the remaining
light bulb is dimmer?
C is a resistor which decreases current and therefore makes the bulb decrease in
brightness.
STANDARD 5.4
5.4. Describe conceptually the attractive or repulsive forces between objects relative to their charges
and the distance between them (Coulomb's law).
10-38 5.4 In a television set with a cathode ray tube display, a beam of negatively charged particles called
cathode rays passes by a positively charged plate. The beam is deflected before it hits the television screen to
produce an image. Which of the following changes would result in the greatest increase in the attraction
between the negatively charged particles in the beam and the positively charged plate?
A. increasing the distance between the plate and the particles and increasing the charge on the plate
B. increasing the distance between the plate and the particles and decreasing the charge on the
plate
C. decreasing the distance between the plate and the particles and increasing the charge on the
plate
D. decreasing the distance between the plate and the particles and decreasing the charge on the
plate
Force increases as distance between decreases. Force increases as charge increases.
9-40 5.4 An electrostatic paint sprayer is used to spray paint evenly
onto the surface of a car. Before the paint is sprayed, the car body is
given a positive charge and the paint droplets are given a negative
charge. The paint droplets experience an attractive force as soon as
they are released from the sprayer. The paint droplets are originally
sprayed at a distance of 30 cm from the car body, as shown.
Which of the following changes will cause the largest increase in the attractive force on the paint droplets?
A. The charge on the car body is doubled. B . The charge on the paint droplets is doubled.
C. The distance between the paint droplets and the car body is halved.
D. The distance between the paint droplets and the car body is doubled.
The smaller the distance the greater the force and it is squared in the equation so that makes it very important.
𝐹=𝐾
𝑞1 𝑞2
𝑑2
8-2 5.4 Two oppositely charged objects are separated by a small distance. The objects are then moved
three times farther apart from each other. Which of the following statements best describes what
happens to the electrical force between the objects?
A. The force of attraction increases.
C. The force of attraction becomes zero.
B. The force of attraction decreases
D. The force of attraction stays the same.
If distance decreases force increases, if distance increases force decreases.
The answer B, may have been a typo on your version.
8-36 5.4
The distance between two charges is represented by d. In which of the following diagrams is the
attractive force between the two charges the greatest?
C Greatest force will be the combination of small distance and large charge.
STANDARD 5.5
5.5. Explain how electric current is a flow of charge caused by a potential difference (voltage) and
how power is equal to current multiplied by voltage.
11-17 5.5
The potential difference across a resistor is 12 V.
When a current of 5 A is flowing through this resistor,
what is the power used by the resistor?
A. 2.4 W
B. 60 W
C. 300 W
D. 1500 W
10-24 5.5
Which of the following actions would increase the
current through a circuit component?
A. decreasing the power in the component
B. increasing the resistance of the component
C. increasing the voltage across the
component
D. placing another identical component in
series in the circuit
Power = Current x Volts
Increasing Voltage increases current and power.
( 12 V ) ( 5 Amps ) = 60 Watts
9-17 5.5
Which of the following would be an advantage of
using a 42 V battery in a car instead of a 12 V battery?
8-14 5.5
The power of a toaster can be determined if which of
the following values are known?
A. It would allow carmakers to use fewer
circuits.
B. It would eliminate the use of generators
and alternators.
C. It would produce the same amount of
power using less current.
D. It would produce the same amount of
power using more current.
A. the dimensions of the toaster
B. the resistance of the toaster’s
insulation
C. the voltage applied to the toaster and
the toaster’s temperature
D. the current through the circuit and the
voltage.
P = IV, If V is increased I can decrease and still
have the same Power.
STANDARD 5.6
5.6. Recognize that moving electric charges produce magnetic forces and moving magnets produce
electric forces. Recognize that the interplay of electric and magnetic forces is the basis for electric
motors, generators, and other technologies.
11-38 5.6 A student is turning the handle of a generator. Another student connects a bulb to the
generator. The bulb lights up. The first student continues to turn the handle of the generator at the
same speed, but finds it harder to turn. Which of the following best explains this?
A. Less mechanical energy is required when the bulb is lit.
B. More energy is put into the generator when the bulb is lit.
C. Less mechanical energy is required the longer the generator is turned and the bulb is lit.
D. The energy requirement of the generator is the same at any speed whether or not the bulb is lit.
The bulb requires energy. When the bulb was not connected the generator was not
creating energy.
10-19 5.6
The diagram below shows copper wire wrapped around a cardboard tube,
which is then attached to a galvanometer. A galvanometer detects and
measures small amounts of electric current.
Which of the following would cause the galvanometer needle to move?
A. wrapping additional wire around the tube
B. uncoiling the wire wrapped around the tube
C. moving a magnet back and forth inside the tube
D. moving an aluminum block up and down inside the tube
Moving a Wire in Magnetic Field creates a current.
9-42 5.6
Precise measuring instruments require shock absorbers to eliminate small vibrations that can affect
the results of an experiment. One type of shock absorber that can be used is an electromagnet that
repels a magnetic platform placed above it.
Which of the following setups would provide the greatest lift to the platform?
Two batteries are more powerful than one so it must be either B or D . D has more coils than B so the
creates a more powerful magnet. The answer must be D.
8-7 5.6 A magnetic compass is placed near an insulated copper wire. When the wire is connected to a
battery, the compass needle changes position. Which of the following is the best explanation for the
movement of the needle?
A.
B.
C.
D.
The copper wire magnetizes the needle to create a force.
The needle magnetizes the copper wire to create a force.
The current in the wire produces a magnetic field and exerts a force on the needle.
The insulation on the wire becomes energized and exerts a force on the needle.
A current in a wire always creates a magnetic field.
OPEN RESPONSE QUESTIONS
11-12
Standard: 5.2 - Develop a qualitative and quantitative understanding of current, voltage,
resistance, and the connections among them (Ohm's law).
An electrician places a variable resistor in series with an LED lamp and a 6 V battery, as shown below.
LED lamps are efficient sources of light that operate at a specified voltage for a
wide range of currents. The LED lamp in this circuit operates at a constant 3 V for
all settings of the variable resistor, while the remaining 3 V is always dropped
across the variable resistor.
a. Calculate the current passing through the variable resistor when it is set to
each of the values shown in the table below. Show your calculations and
include units in your answers.
Don’t be nervous or confused by the paragraph above. Simply use
Ohm’s Law for each example listed in the table.
In each case I = V/R
Voltage (V)
Resistance (Ohms)
3.0
4
3.0
Current (A)
𝑉 3𝑉
𝐼= =
𝑅 4𝛺
Calculated Current
.75 Amp
6
𝐼=
𝑉 3𝑉
=
𝑅 6𝛺
.5 Amp
3.0
10
𝐼=
𝑉
3𝑉
=
𝑅 10𝛺
.3 Amp
3.0
15
𝐼=
𝑉
3𝑉
=
𝑅 15𝛺
.2 Amp
3.0
20
𝐼=
𝑉
3𝑉
=
𝑅 20𝛺
.15 Amp
b. On the grid in your Student Answer Booklet, make a graph using your answers to part (a). Current
should be on the y-axis and resistance should be on the x-axis. Clearly label the axes and use a proper
scale.
Current vs Resistance
0.8
Current (Amps)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
5
10
15
20
25
Resistance (Ohms)
c. Based on the graph, describe what happens to the LED lamp as the resistance decreases.
The maximum recommended current for the LED lamp is 0.3 A.
The led becomes brighter as the variable resistor decreases in value. This allows more voltage for the light,
which creates more current and a brighter light.
d. If the LED lamp is operated for a long time with the variable resistor set at 4 Ω, describe the most
likely effect on the LED lamp.
The current will be higher than the recommended current and will eventually burn out the light.
10-45
Standard: 5.5 - Explain how electric current is a flow of charge caused by a potential difference
(voltage) and how power is equal to current multiplied by voltage.
The diagram below shows a circuit with a 12 V battery connected in series with a 4
resistor and a 2 resistor. Two points in the circuit are labeled X and Y.
a. Calculate the current in the circuit. Show your calculations and include units
in your answer.
First determine the total resistance:
4Ω +2Ω = 6Ω
Now use Ohm’s Law to determine the Current:
I = V/R = 12 V / 6 Ω = 2 Amps
b. Calculate the voltage drop across the 4
answer.
resistor. Show your calculations and include units in your
Use Ohm’s Law for each Resistor: V = IR
V = (2 Amps) ( 4 Ω) = 8 Volts
and
V = (2 Amps) ( 2 Ω) = 4 Volts
c. Determine the voltage drop between point X and point Y. Explain the reasoning for your answer.
No voltage drop occurs in a wire.
d. Calculate the power of the entire circuit. Show your calculations and include units in your answer.
P = IV = (2 Amps)( 12 V) = 24 Watts
9-23
Standard: 5.4 - Describe conceptually the attractive or repulsive forces between objects relative to their charges and the
distance between them (Coulomb's law).
In the diagram below, shaded circles 1, 2, and 3 represent fixed charged objects, and circle 4 represents a charged object
that is free to move.
The magnitude of all the charges is equal.
a.
Describe how charged objects 1, 2, and 3 will each affect object 4.
1 attracts 4 ( opposite charges attract)
2 repels 4 ( like charges repel)
3 repels 4 ( like charges repel)
b. Compare the magnitude of the electric force between object 3 and object 4 with the magnitude of the electric force
between object 2 and object 4.
The force between 3 & 4 is less than the force between 2 & 4 because 3 is at a greater distance than 2. The closer the
charges are the greater the force.
c.
Draw a diagram to show where object 4 will most likely move in relation to fixed objects 1, 2, and 3. Explain your
answer.
8-45
Standard: 5.3 - Analyze simple arrangements of electrical
components in both series and parallel circuits. Recognize symbols
and understand the functions of common circuit elements
(battery, connecting wire, switch, fuse, resistance) in a schematic
diagram.
A circuit with three identical light bulbs is shown in the diagram
below.
a. Identify the symbol labeled J in the circuit.
J is a battery.
b. Describe what each light bulb does in each of the following situations:




when switches 1 and 2 are open
when switches 1 and 2 are closed
when switch 1 is open and switch 2 is closed
when switch 1 is closed and switch 2 is open
NOTE: Open switches do not allow electricity to flow.

when switches 1 and 2 are open
When 1 and 2 are open, no electricity can make it to X or Y so they will not light. Z will still light.

when switches 1 and 2 are closed
When 1 and 2 are closed, electricity will make it to all bulbs so all will light.

when switch 1 is open and switch 2 is closed
Z will be lit. If 1 is open nothing can make it to 2 either. So only Z will light.

when switch 1 is closed and switch 2 is open
Y and Z will light.
7-11
Standard: 5.1 - Recognize that an electric charge tends to be static on insulators and can move on and in conductors. Explain
that energy can produce a separation of charges.
A student rubs a balloon on her hair and the balloon acquires a negative charge.
a. Explain why the balloon acquires a negative charge.
The balloon gains electrons.
b. After the balloon is rubbed on the student's head, the student's hair stands out from her head. Explain
why this happens.
The hair is charged due to loss of electrons. Opposites repel.
The student then brings the negatively charged balloon near another balloon that has charged the same
way.
c. Describe and explain what happens when the negatively charged balloon is brought near another
negatively charged balloon.
The balloons repel because they are both negatively charged. Like charges repel.