Chapter 9~ Electric Current, Potential Difference And Resistance

Question 1

What direction does the conventional current 💫 flow?

Answer 1

From positive to negative. (from higher potential to lower potential)

Question 2

Conduction /free electrons are

Answer 2

Mobile electrons that can carry (borne) an electric current. This allows a metal to conduct an electric current.

Question 3

Why is the conventional current wrong 💫? (explain in 2 points for simplicity)

Answer 3

📌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 💫

Question 4

What is an electrolyte?

Answer 4

A solution which conducts and contains both positive and negative ions.
These move in opposite direction when the solution is connected to a cell.

Question 5

What is an electrolyte?

Answer 5

A solution which conducts and contains both positive and negative ions.
These move in opposite direction when the solution is connected to a cell.

Question 6

What are charge carriers ➕➖🚗❔

Answer 6

Any charged particles which contribute to an electric current. These can be electrons, protons or ions.

Question 7

Definition of electric current :

Answer 7

Electric current is the rate of flow of electric charge past a point.

Question 8

Definition of a coulomb :

Answer 8

° 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.

Question 9

The elementary charge e =

Answer 9

1.6 × 10^-19 C

Question 10

The current formula in relation to its definition :

Answer 10

Current = charge/time

❤️I = Q/t❤️

Question 11

Formula for charge in relation to current and time ⌚

Answer 11

❤️Q= I×t❤️
Charge = current ×time

Question 12

The change in charge (Q=I× t) formula is…

Answer 12

🔼Q= I ×🔼 t

Question 13

How is the elementary charge represented for protons and electrons?

Answer 13

Proton = + 1.6 × 10^-19 C

Electron = - 1.6 × 10^ - 19 C

Question 14

Formula for Charge( in terms of subatomic particles) =

Answer 14

❤️Q=nq❤️
❤️Q=ne❤️

n-number of e-‘s
e/q- total charge of e-

Question 15

Charge is ‘quantised’. What does quantised refer to?

Answer 15

Can only come in amounts which are integer multiples of the elementary charge.

Integer - a number which is not a fraction, a whole number.

Question 16

For the formula:
I=nAvq
I =nAve
What do all the variables stand for?

Answer 16

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

Question 17

Number density refers to…?

Answer 17

The number of conduction e-‘s per unit volume

Question 18

Deriving I =nAve (or I =nAvq) in 4 steps

Imagine a wire with length, l ; cross sectional area, A; current, I ; and electrons

Answer 18

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)

Question 19

Definition of mean drift velocity :

Answer 19

°the average speed of a collection of charged particles when current flows.

Question 20

What causes the collection of e-‘s to have a drift velocity instead of just a velocity?

Answer 20

It’s haphazard journey (e-‘s randomly collide with fixed but vibrating metal ions)

Question 21

Think of equation v = I/(nAq)

Name which variables the drift velocity is proportional to or indirectly proportional to…

Answer 21

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

Question 22

Define a volt :

Answer 22

A volt is defined as one joule per coulomb.

1V= 1JC^-1

Question 23

Define E. M. F and the formula

Answer 23

E. M. F is the work done per unit charge when other forms of energy are converted to electrical energy.

❤️E = W/Q❤️

Question 24

Define p.d. And the formula for it in terms of its definition :

Answer 24

p.d. Is the work done per unit charge when electrical energy is converted to other forms.

❤️V = W/Q❤️

Question 25

The size of the current depends on two factors if you connect a lamp to a battery :

Answer 25

1. The potential difference / voltage across the lamp⚡(the 👆 it is the 👆 the current)
2. The resistance of the lamp ( the 👆 this is the 👇 the current)

Question 26

The definition of resistance and the formula that is linked to it :

Answer 26

° the resistance of any component is defined as the ratio of the potential difference to the current.

R= V/I

Question 27

Resistance is measured in?

Answer 27

Ohms ♎

Question 28

Definition of the ohm ♎

Answer 28

°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

Question 29

Definition of power and the formula that relates to it :

Answer 29

°The rate of work done or the rate at which energy is transferred.

Power = energy transferred / time taken

P=W/🔼t

Question 30

Work done is the same as

Answer 30

Energy transferred

Question 31

The 5 formulae for power :

Answer 31

1. P= W/🔼 t
2. P=VI
   Power = potential difference × current
3. P = I^2 × R
   Power = current squared × resistance
4. P=V^2 /R
   power = voltage squared ÷ resistance
5. P = Fv

Question 32

Definition of a fuse

Answer 32

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.

Question 33

High currents cause wires to get hot 🔥 which can lead to 3 examples of things

Answer 33

Damaged wires, fumes from melting insulation and even fires 🔥

Question 34

Purpose a fuse

Answer 34

Stop any hazardous current by melting and breaking the circuit 💫

Question 35

Definition of dissipated

Answer 35

Energy being transferred

Question 36

Energy transferred (work done) in a circuit in a time 🔼t is given by?

Formula W=

Answer 36

❤️W= IV🔼t❤️

Work done (energy transferred) =

current × voltage ⚡ × change in time ⌚

Question 37

A formula for efficiency =

Answer 37

V/E ×100

V- p.d. V= E-IR

E- emf