Measuring Electric Current
What are amperes, volts, and ohms?
How do you measure temperature? In degrees. You measure time in
minutes, hours, days etc. How do you measure length? Weight?
We use different units to measure different things. There are special
units to measure electricity too. Three of the most important are
ampere, volt, and ohm.
Amperes - The size of an electric current depends on how many
electrons pass a point in a circuit every second. The greater the number
of electrons, the larger the current. Fewer electrons mean a smaller
current.
Volts - nothing moves by itself. A force is needed to make something
move. Electricity needs a force to move it. Electrons move in a circuit
because a force pushes them. The name for the force or pressure that
pushes electrons is electromotive force. It is often called EMF. The
strength of the EMF is measured in volts.
OHMS - ohms measure the resistance to the flow of electrons. You
know that a wire resists the flow of electrons. The amount of resistance
is measured in ohms.
There is a connection between amps, volts, and ohms. When one
changes, there must be a change in one or both of the others. There is a
rule for figuring these changes. It is called Ohm’s Law.
VOLTS
AMPERES (AMPS)
The force that moves electrons The number of electrons that
in a circuit
are moving
OHMS
Resistance – the force that
tries to stop or slow the
electrons
The number of electrons passing a point in a wire every second is one ampere of current.
Which one is easier to say – one ampere or 6,281,000,000,000,000,000 electrons?
Different electrical devices use different amperes.


A 100-watt light bulb uses about 1 ampere.
An electric iron or broiler uses about 10 to 12 amperes.
Fill in the correct answer for each of the following:
1. Another name for electric current is
.
2. Amperes tell us how many
move past a point in a circuit every second.
3. EMF stands for
.
4. Electrical force of pressure is measured in units called
.
5. Electrical resistance is measured in units called
.
Use your own words to explain each of the following:
1. EMF
2. VOLTS
3. AMPERES
4. OHMS
Match each term in Column A with its description in Column B. Write the correct letter in
the space provided.
Column A
Column B
Volts
Amps
Circuit
Ohm’s Law
Ohms
a) electrical resistance
b) path for moving electrons
c) relationship between volts, amps, and ohms
d) electrical pressure
e) number of electrons passing a point in a wire
In the space provided, write “true” if the sentence is true. Write “false” if the sentence is
false.
1. EMF stands for a number of electrons.
2. Another name for resistance is ampere.
3. Volts measure electrical pressure of force.
4. Different circuits have different amps, volts, and ohms.
5. If volts change, then amps and ohms stay the same.
Below are several scrambled words you have used in this lesson. Unscramble the words and
write your answers in the spaces provided.
1. PREAME
2. SEPRURES
3. MOH
4. TOLV
5. TRENRUC
Choose the correct word or term for each statement. Write your choice in the spaces
provided.
1. Electricity that is not moving is called
2. Electricity that is moving is called
3. Friction produces
4. A dry cell produces
5. The electricity we use is
6. Current electricity is the flow of
7. Most current electricity comes from
electricity. (static, current)
electricity. (static, current)
electricity. (static, current)
electricity. (static, current)
electricity. (static, current)
. (atoms, electrons)
. (generators, batteries)