Chapter 12 - Electric current #1 Flashcards
What is current?
The rate of flow of charge. The amount of charge carriers flowing through a point per unit time.
Current is due to the movement of charge carriers (flow of charge).
In a metallic conductor, the charge carriers are _______ _______. When a voltage is applied across the metal, these ________ ________ are attracted towards the _______ terminal of the metal.
In a metallic conductor, the charge carriers are conduction electrons (delocalised electrons in metal). When a voltage is applied across the metal, these conduction electrons are attracted towards the positive terminal of the metal.
In an insulator, each electron is ________ to an atom and ______ move away from the atom. When a voltage is applied across an insulator, _________ passes through it because _______ can _____ through the insulator.
In an insulator, each electron is attracted to an atom and cannot move away from the atom. When a voltage is applied across an insulator, no current passes through it because no electrons can move through the insulator.
What is potential difference?
The work done (or energy transferred) per unit charge.
Electrons (charge carriers) receive energy at the battery and carry it around the circuit.
When an electron passes through a component, it does work passing through it and so deposits some or all of its energy.
What are the equations for potential difference?
W
V = ——
Q
V = IR
ε = I(R + r) = V + Ir
What is the equation for electrical energy produced when charge Q passes through a source?
E = Qε
What is the equation for work done by charge carriers?
W = IVt
or
W = Pt
What is resistance caused by?
The repeated collisions between charge carriers passing through the component and the positive ions in the component vibrating about fixed positions in the component.
Unless specifically stated in questions, ammeters and
voltmeters should be treated as…
…ideal (having zero and
infinite resistance respectively).
Voltmeters (infinite resistance)
Ammeters (zero resistance)
What is Ohm’s Law?
The pd across a metallic conductor is directly proportional to the current under constant physical conditions.
I ∝ V
How does the resistance of a metal change with increase of temperature? Explain why.
The resistance of a metal increases with increase of temperature.
This is because the positive ions in the conductor vibrate more when its temperature is increased so the charge carriers cannot pass through the metal as easily.
What are charge carriers?
Charged particles that move through a substance when a pd is applied across it (e.g. electrons).
Work done by charge carrier to pass through component =
Work done by charge carrier to pass through component = Energy loss of charge carrier
Ammeters are connected in ______ to a component.
Ammeters are connected in series to a component.
Voltmeters are connected in ______ to a component.
Voltmeters are connected in parallel to a component.
