Section 5 - Electricity: 5.1 - Current Electricity Flashcards
What is electric current? State its units.
The rate of flow of charge. It is measured in
amperes (amps).
What is potential difference?
The work done moving a unit charge between 2 points in a circuit
V = W / Q
What is resistance?
How difficult it is for current to flow through an
appliance.
A component has a resistance of 1Ω if 1A flows
through it when a p.d of 1V is applied across it.
R = V / I
What is meant by an ohmic conductor?
A conductor that obeys Ohm’s law, meaning that
current is directly proportional to potential
difference providing physical conditions (such as
temperature) remain constant.
How can you measure the current in a circuit?
You can measure the current in a circuit with an
ammeter connected in series with the
component.
How do you measure potential difference across a
component?
Using a voltmeter, connected in parallel across
the component being measured.
What does the gradient of a current-potential
difference graph represent?
Rate of change of current with respect to voltage.
This is not the same as 1/R
Does this graph represent an ohmic conductor?
(Insert graph)
Yes, as the line has a
constant gradient and
passes through the origin.
This shows that voltage is
directly proportional to
current.
Which graph represents an appliance with higher
resistance? (Insert graphs A and B)
B
A higher voltage is required in
B for the same change in
current in comparison to A.
What common appliance could this curve represent?
(Insert graph)
A filament lamp. As the
current increases the the
resistance also increases.
A big increase in the
voltage produces only a
small increase in current
Why does the current increasing on a filament lamp
cause an increase in the resistance?
As current flows through the lamp, electrical energy
is converted to heat energy so the metal ions vibrate
with increased amplitude. This impedes the
movement of electrons through the lamp as they
collide with the ions (resistance has increased).
What is a diode? What does the graph look like?
A diode is a appliance that only allows current to
flow in one direction.
(Insert graph)
Unless stated in the question, should you assume
that voltmeters to have zero resistance or infinite
resistance?
You should assume they have infinite resistance. Current
takes the path of least resistance so, if the voltmeter has
infinite resistance, when applied in parallel to the appliance,
no current will flow through it and all the current will flow
through the appliance.
Why should you assume that an ammeter has zero
resistance unless stated otherwise?
This assumption means that there would be 0
potential difference across the ammeter and no
energy is lost across it; it does not affect the
circuit.
What is an Light Dependent Resistor (LDR)?
A semiconductor that is sensitive to light.
As the light intensity increases, its resistance
decreases.