Chapter 9~ Electric Current, Potential Difference And Resistance Flashcards
Definitions, key ideas 💡 and formulae
What direction does the conventional current 💫 flow?
From positive to negative. (from higher potential to lower potential)
Conduction /free electrons are
Mobile electrons that can carry (borne) an electric current. This allows a metal to conduct an electric current.
Why is the conventional current wrong 💫? (explain in 2 points for simplicity)
📌When a cell is connected to a wire, it exerts an electrical force on the mobile electrons that makes them travel along the length of the wire.
📌Since e-‘s are negatively charged, they flow away from the negative terminal and towards the positive terminal which is opposite to the conventional current 💫
What is an electrolyte?
A solution which conducts and contains both positive and negative ions.
These move in opposite direction when the solution is connected to a cell.
What is an electrolyte?
A solution which conducts and contains both positive and negative ions.
These move in opposite direction when the solution is connected to a cell.
What are charge carriers ➕➖🚗❔
Any charged particles which contribute to an electric current. These can be electrons, protons or ions.
Definition of electric current :
Electric current is the rate of flow of electric charge past a point.
Definition of a coulomb :
° one coulomb is the charge which flows past a point in a circuit 💫 in a time of 1 s when the current is 1 A.
The elementary charge e =
1.6 × 10^-19 C
The current formula in relation to its definition :
Current = charge/time
❤️I = Q/t❤️
Formula for charge in relation to current and time ⌚
❤️Q= I×t❤️ Charge = current ×time
The change in charge (Q=I× t) formula is…
🔼Q= I ×🔼 t
How is the elementary charge represented for protons and electrons?
Proton = + 1.6 × 10^-19 C
Electron = - 1.6 × 10^ - 19 C
Formula for Charge( in terms of subatomic particles) =
❤️Q=nq❤️
❤️Q=ne❤️
n-number of e-‘s
e/q- total charge of e-
Charge is ‘quantised’. What does quantised refer to?
Can only come in amounts which are integer multiples of the elementary charge.
Integer - a number which is not a fraction, a whole number.
For the formula:
I=nAvq
I =nAve
What do all the variables stand for?
I- current
n-number density ( the number of conduction e-‘s per unit volume)
v- mean drift velocity (of e-‘ s)
e/q- elementary charge
Number density refers to…?
The number of conduction e-‘s per unit volume
Deriving I =nAve (or I =nAvq) in 4 steps
Imagine a wire with length, l ; cross sectional area, A; current, I ; and electrons
Step 1: Number of e-‘s = number density × volume of wire
❤️Number e-‘ s = n × A × l❤️
Step 2: Q= ne
Charge of e’s = number of e-‘s × electron charge
❤️Charge of e-‘ s = n ×A × l × e ❤️
Step 3 : we can find current bec I = Q/t
So,
Current, I= (n×A× l ×e) / t
And l/t is the same as
length(displacement ) /time which is velocity
Step 4 : therefore
❤️I = nAve or I= nAvq❤️ (for general cases)
Definition of mean drift velocity :
°the average speed of a collection of charged particles when current flows.
What causes the collection of e-‘s to have a drift velocity instead of just a velocity?
It’s haphazard journey (e-‘s randomly collide with fixed but vibrating metal ions)
Think of equation v = I/(nAq)
Name which variables the drift velocity is proportional to or indirectly proportional to…
v ♉ I (v is directly proportional to I)
v ♉ 1/A (v is indirectly proportional to A)
v ♉ 1 / n ( v is indirectly proportional to n)
♉ Means proportional
Define a volt :
A volt is defined as one joule per coulomb.
1V= 1JC^-1
Define E. M. F and the formula
E. M. F is the work done per unit charge when other forms of energy are converted to electrical energy.
❤️E = W/Q❤️
Define p.d. And the formula for it in terms of its definition :
p.d. Is the work done per unit charge when electrical energy is converted to other forms.
❤️V = W/Q❤️
The size of the current depends on two factors if you connect a lamp to a battery :
- The potential difference / voltage across the lamp⚡(the 👆 it is the 👆 the current)
- The resistance of the lamp ( the 👆 this is the 👇 the current)
The definition of resistance and the formula that is linked to it :
° the resistance of any component is defined as the ratio of the potential difference to the current.
R= V/I
Resistance is measured in?
Ohms ♎
Definition of the ohm ♎
°The ohm is the resistance of a component when a potential difference of 1 volt drives a current of 1 ampere through it.
°1 ohm is equivalent to ‘1 volt per ampere’
1♎= 1VA^-1
Definition of power and the formula that relates to it :
°The rate of work done or the rate at which energy is transferred.
Power = energy transferred / time taken
P=W/🔼t
Work done is the same as
Energy transferred
The 5 formulae for power :
- P= W/🔼 t
- P=VI
Power = potential difference × current - P = I^2 × R
Power = current squared × resistance - P=V^2 /R
power = voltage squared ÷ resistance - P = Fv
Definition of a fuse
A small, thin conductor designed to melt and separate into two pieces for the purpose of breaking a circuit 💫 in the event of an excessive current.
High currents cause wires to get hot 🔥 which can lead to 3 examples of things
Damaged wires, fumes from melting insulation and even fires 🔥
Purpose a fuse
Stop any hazardous current by melting and breaking the circuit 💫
Definition of dissipated
Energy being transferred
Energy transferred (work done) in a circuit in a time 🔼t is given by?
Formula W=
❤️W= IV🔼t❤️
Work done (energy transferred) =
current × voltage ⚡ × change in time ⌚
A formula for efficiency =
V/E ×100
V- p.d. V= E-IR
E- emf
