S6 electricity - 1. current, potential difference and resistance Flashcards
what is current?
current is the rate of flow of charge
which direction does conventional current flow?
conventional current flows from + to - of the cell (the opposite direction of electron flow)
define one coulumb
one coulomb (C) is the amount of charge that passes in one second if the current is 1 ampere (A)
what is an ammeter used for?
Ammeters are used to measure the current flowing through a component
Potential difference is…
the energy per unit charge
which direction do electrons flow?
Electrons flow from - to + of the cell (opposite to conventional current)
what is a coulomb?
A coulomb is the unit of charge
An ammeter always goes in…
SERIES to measure current flow.
what is voltage?
Voltage is the energy per unit charge.
A voltmeter always goes in…
parallel
an ideal ammeter has…
no resistance at all. its 0
an ideal voltmeter has…
infinite resistance
why is it important that an ideal voltmeter has infinite resistance?
An infinite resistance ensures that no current is drawn, hence giving accurate readings of potential difference (V).
why is it important to have an ideal ammeter?
resistance affects the measured amperage therefore if it’s 0 it wouldn’t affect the measured amperage.
what is potential difference?
Potential difference is the energy per unit charge
define potential difference
Potential difference (V) is defined as the work done per unit charge moved.
what is a voltmeter used for?
A voltmeter is used to measure the potential difference across a component
state the definition of the volt
The potential difference across a component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through the component.
state the equation for potential difference (V)
V =IR
V (voltage - potential difference)
I (current)
R (resistance)
what is resistance measured in?
Resistance is measured in ohms (Ω)
state ohms law
Provided the physical conditions, such as temperature, remain constant, the current through an ohmic conductor is directly proportional to the potential difference across it
write the formula for current (not V=IR)
I = ΔQ / Δt
ΔQ is the charge in coulombs
Δt is the time taken in seconds
what is potential difference measured in?
potential difference is measured in volts (V)
what is current measured in?
Current is measured in amperes (A)
define resistivity
Resistivity is a measure of the resisting power of a specified material to the flow of electric current.
what is an ohmic conductor?
conductors that obey ohms law (mostly metals) are called ohmic conductors.
state the formula for potential difference
V = W/Q
