17) Current of Electricity Flashcards
Define current.
Current is the rate of flow of charges.
What is the SI unit of current?
Ampere (A)
What is the instrument used to measure current in a circuit?
Ammeter
What is the relationship between I, Q and t?
(in other words the formula)
[Please recall what I, Q and t represents]
Q = It
How should the ammeter be connected in a circuit?
connected in series
Define electromotive force (e.m.f.).
Electromotive force (e.m.f.) is the amount of work done by a source (e.g. battery, cell) in driving a unit charge around a complete circuit.
Define potential difference (p.d).
Potential difference (p.d.) across a component in a circuit is the work done to drive a unit of charge through the component.
What is the SI unit of electromotive force (e.m.f.)?
Volt (V)
What is the SI unit of potential difference (p.d)?
Volt (V)
What is the instrument used to measure voltage across a component in a circuit?
voltmeter
What is the relationship between V, W and Q?
(in other words the formula)
[Please recall what V, W and Q represents]
W = VQ
How should the voltmeter be connected in a circuit?
connected in parallel to the component
Define resistance.
Resistance of a component is the ratio of voltage to current in a component.
What is the relationship between R, V and I?
(in other words the formula)
[Please recall what R, V and I represents]
R = V / I
What is the SI unit of resistance?
ohm (Ω)
What are the factors that affect the resistance of a wire?
[There are 4 factors.]
1) length of wire (l)
2) cross-sectional area of wire (A)
3) resistivity of the material (ρ)
4) temperature of wire
Define Ohm’s Law.
Ohm’s law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remains constant.
Explain why the filament lamp does not obey Ohm’s law.
As current flows through the filament lamp, it heats up and increases the resistance of the filament lamp.
What are the 2 factors on a VI graph that shows an electrical component obeys Ohm’s law?
(i.e. what are the 2 things to look out for in a VI graph?
1) The graph must be a straight line.
2) The line must pass through the origin.
State how the length of wire affects the resistance.
The longer the wire, the larger the resistance.
State how the thickness of wire affects the resistance.
thickness also means cross-sectional area of wire
The thicker the wire, the lower the resistance.
The thinner the wire, the higher the resistance.
State how temperature of a wire affects its resistance.
The higher the temperature, the larger the resistance.
State the formula to find the total resistance of resistors connected in series.
Rt = R1 + R2 + R3
State the formula to find the total resistance of resistors connected in parallel.
1/Rt = 1/R1 + 1/R2 + 1/R3
