Transcript voltage_and_current

Pushing around
• Electromotive force (E.M.F.)
• Potential Difference
Electromotive Force (E.M.F.)
Show on this circuit diagram the places where the electrons lose
energy and draw an arrow for the direction of the electrons.
Electrons lose energy
Electromotive Force (E.M.F.)
Show on this circuit diagram the places where the electrons gain
energy and draw an arrow for the direction of the current.
Electrons gain energy
Electromotive Force (E.M.F.)
A cell/battery provides the energy to the electrons to move around
the circuit (a bit like a water pump pushing the water around a
house). This electrical pressure is called Electromotive Force
(E.M.F.). The E.M.F. is measured in Volts (V).
Electrons
move this
way!
Electrons gain energy
Electrons lose energy
Direction
of the
current!
Potential difference (Voltage)
How do the electrons lose energy inside the light bulbs?
The electrons give up their energy when passing through the thin
wires in the light bulbs. That is how the filament inside the lamp
gets hot and glows.
It’s a bit like a waterfall. The water has more energy at the
top than at the bottom because there has been a fall in
gravitational energy and the water loses energy when
hitting the ground. This difference of electrical pressure
across the bulbs is called Potential Difference (p.d.), or
VOLTAGE
Higher gravitational energy
Lower gravitational energy
The water can’t get back
up on its own. It has lost
energy as heat and sound.
Electromotive Force (E.M.F.)
Now put this circuit together and measure the potential difference
across each light bulb and the E.M.F. across the cell.
What do you notice?
The sum of all the drops in voltage must be
equal to the gain in E.M.F. given by the
power source (cell).
In other words, all the energy spent in the
bulbs must be regained in the cell to keep
the flow of electrons.