2.1 Conduction of electricity Flashcards
What is electrical current?
rate of flow of charge
What is conventional current?
the flow of a positive charge from positive to negative and is the reverse of real electron flow
What is electron flow?
the flow of a negative charge from negative to positive
How to work out current?
current = change in charge ÷ change in time
I (amps) = △Q (coulombs) ÷ △T (seconds)
How to work out the change in charge?
change in charge = current x change in time
△Q = I x △T (ONLY WORKS WHEN CURRENT IS CONSTANT)
How to work out the change in time
change in time = change in charge ÷ Current
△T = △Q ÷ I
What is the total charge in a current - time graph?
Area under the line
In metals, what does electrons do?
they move to make a current
What is the charge of one electron?
1.6 x 10⁻¹⁹ coulombs
Q. A current of 2.4 amps. How many electrons have flowed past a point in 5 minutes?
5 mins = 300 seconds
△Q = I x △T
= 2.4 x 300
= 720 coulombs
number of electrons = 720 ÷ 1.6 x 10 ^ -19
= 4.5 x 10^21What is electric current?
Rate of flow of charge
How to work out number of electrons?
charge (C) ÷ 1.6 x 10⁻¹⁹
What is the unit of battery capacity?
Ah (amp hours)
What does a battery of 70Ah means?
the battery can supply 1 amp for 70 hours, or 2 amps for 35 hours, or 10 amps for 7 hours… It has a battery capacity of 70 x 3600 = 252000 C per hour.
What is drift velocity?
the average velocity attained (gained) by charged particles (e.g electrons)
what is drift velocity measured in?
ms⁻¹ meters per seconds
What is the pre condition for the electrons to move with a drift velocity?
When a potential difference(voltage) is applied across the wire.
How to calculate volume of a wire?
Avt m³
A = cross sectional area[m²] (π r²) vt = distance [m] (velocity x time)
How to calculate the number of electrons?
nAvt
n = number of free electrons per m³ Avt = volume (m³)
How to calculate the charge in the volume?
nAvte
n = number of free electrons Avt = volume e = the charge of an electron [1.6 x 10⁻¹⁹] C
How to calculate the current?
Current = nAvte ÷ t ( change in charge ÷ change in time)
both t cancels each other, therefore
Current = nAve
How to calculate drift velocity?
V = I ÷ Ane
Does the current change in the narrow section?
No, Current is the rate at which electric charge flows past a point, meaning that it doesn’t get used up by components therefore always stays the same.
Does the velocity change in the narrow section?
Yes, velocity is inversely proportional to area,
V ∝ 1 / A meaning that the bigger the area, the smaller the velocity and vice versa
