Download Role of a battery

Voltage
Voltage = Energy
Voltage = energy
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To make a light bulb light up, you need to supply
energy. Where does this energy come from?
That’s right, a battery (or the house current if
the lamp is plugged in). We will focus on the
battery situation, though.
Role of a battery
The role of the battery is to:
1. Supply the energy to do
WORK upon the charge to
move it.
2. Pump the charge from – to + terminal
within the battery.
3. Maintain a voltage difference across the
external circuit (wires, bulbs, etc.)
Some background…
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Each electron carries kinetic energy. This
energy is measured by a unit called a volt.
The number of electrons is measured by the
charge, in coulombs.
A volt is the measure of the energy level
anywhere in a circuit.
The battery does not supply electrons nor
protons to the circuit; those are already present
in the atoms of the conducting material (usually
copper).
Electrical potential difference
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There is a positive terminal of the battery and a
negative terminal. The positive end is the high
potential and the negative end is the low
potential. Electricity, like water, moves from a
place of high potential to a place of low
potential.
Once the charge reaches the high potential end, it
will naturally flow through the wires to the low
potential terminal.
Voltage is sometimes called electrical potential
difference. The potential difference of a
fresh D cell battery is 1.5 volts.
How voltage works
The little men (charges) leave the battery at the
positive end. They are carrying full beakers of
energy. The energy is used up to light the bulb.
The charges with empty beakers return to the
negative end of the battery where they climb
the stairs (pumped up) and pick up more
energy.
Water analogy
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Work must be done on the water to move it
from a location of low gravitational potential to
a location of high gravitational potential. This
work requires energy. This work is usually done
by a pump. The pump is the battery. The
energy is called voltage.
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Once the water reaches a
high gravitational
position, it naturally flows
to the low position. No
pump is needed.
Check Your Understanding-1
1. Moving an electron within an
electric field would change the ____
the electron.
A. mass of
B. amount of charge on
C. potential energy of
CYU-1
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C. A force is required to move an electron with
the electric field and thus increases its electrical
potential energy. On the other hand, an electron
moving opposite the direction of the electric
field will decrease its electrical potential energy.
Check Your Understanding-2
2. If an electrical circuit were analogous to a water
A.
B.
C.
D.
E.
circuit at a water park, then the battery voltage
would be comparable to _____.
the rate at which water flows through the circuit
the speed at which water flows through the circuit
the distance which water flows through the circuit
the water pressure between the top and bottom of
the circuit
the hindrance caused by obstacles in the path of
the moving water
CYU-2
D. The battery establishes an electric potential
difference across the two ends of the external
circuit and thus causes the charge to flow. The
battery voltage is the numerical value of this
electric potential difference. In an analogous
manner, it is the difference in water pressure
between the top of the water slide and the bottom
of the water slide that the water pump creates. This
difference in water pressure causes water to flow
down the slide. Because of the similarity between
electric potential difference in an electric circuit and
water pressure in a water park, the quantity electric
potential difference is sometimes referred to as
electric pressure.
Check Your Understanding-3
3. If the electrical circuit in your iPod were
analogous to a water circuit at a water park,
then the battery would be comparable to ____.
A. the people which slide from the elevated
positions to the ground
B. the obstacles which stand in the path of the
moving water
C. the pump which moves water from the ground
to the elevated positions
D. the pipes through which water flows
E. the distance which water flows through the
circuit
CYU - 3
C. The battery in an electric circuit supplies the
energy to pump the charge from its low energy
terminal to the high energy terminal, thus
providing a means by which the charge can flow.
In an analogous manner, a water pump in a
water park supplies the energy to pump the
water from the low energy position to the high
energy position. Because of the similarity
between the battery in an electric circuit and a
water pump in a water park, the battery is
sometimes referred to as a charge pump.
Check Your Understanding-4
4. Which of the following is true about the electrical circuit in a
flashlight?
A.
Charge moves around the circuit at a fraction of the speed
of light.
B.
The batteries supply the charge (electrons) which move
through the wires.
C.
The batteries supply the charge (protons) which move
through the wires.
D. The charge becomes used up as it passes through the light
bulb.
E.
The battery supplies energy which raises charge from low to
high voltage.
F.
... nonsense! None of these are true.
CYU-4
E. As emphasized before, the battery supplies the energy
to move the charge through the battery, thus
establishing and maintaining an electric potential
difference. The battery does not supply electrons nor
protons to the circuit; those are already present in the
atoms of the conducting material. In fact, there would
be no need to even supply charge at all since charge
does not get used up in an electric circuit; only energy is
used up in an electric circuit.
Check Your Understanding-5
5. If a battery provides a relatively high voltage, it
can:
A. do a lot of work over the course of its lifetime
B. do a lot of work on each charge it encounters
C. push a lot of charge through a circuit
D. last a long time
CYU-5
B. The electric potential difference or voltage of a
battery is the potential energy difference across
its terminals for every Coulomb of charge. A
high voltage battery maximizes this ratio of
energy/charge by doing a lot of work on each
charge it encounters.