Electric current
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Define electric current in terms of charge carriers.
Electric current is the rate of flow of charge carriers. It represents the amount of charge passing a point in a circuit per unit time.
What does it mean for charge to be 'quantised'?
Charge is quantised, meaning it exists in discrete units. The smallest unit of charge is the elementary charge (e), the magnitude of the charge of an electron or proton.
State the formula that relates charge (Q), current (I), and time (t).
The relationship between charge, current, and time is given by: Q = It, where Q is charge (in Coulombs), I is current (in Amperes), and t is time (in seconds).
A wire carries a current of 2A for 5 seconds. Calculate the total charge that flows through the wire.
Using Q = It, the total charge is Q = (2 A) * (5 s) = 10 C. Therefore, 10 Coulombs of charge flows through the wire.
State the formula that relates current (I) to the number density of charge carriers (n), area (A), drift velocity (v), and charge (q).
The current is related to the properties of the charge carriers by: I = Anvq, where A is the cross-sectional area of the conductor, n is the number density of charge carriers, v is the average drift velocity of the charge carriers, and q is the charge of each carrier.
Describe what 'number density of charge carriers' represents.
The 'number density of charge carriers' (n) represents the number of free charge carriers (
A copper wire has a cross-sectional area of 1.0 x 10⁻⁶ m², a number density of electrons of 8.5 x 10²⁸ m⁻³, and carries a current of 1.5 A. Calculate the drift velocity of the electrons.
Using I = Anvq, we can rearrange for v: v = I / (Anq). v = (1.5 A) / (1.0 x 10⁻⁶ m² * 8.5 x 10²⁸ m⁻³ * 1.6 x 10⁻¹⁹ C) = 1.1 x 10⁻⁴ m/s.
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