Current of electricity

Question 1

What is an electric current

Answer 1

Electric current, I, is defined as the rate of flow of electric charge through a given cross-section of conductor

Question 2

SI unit of current

Answer 2

Ampere (A)

Question 3

Formula for current

Answer 3

I = Q/t

I - Electric current (A)
Q - Charge (C)
t - Time (s)

Question 4

Difference between conventional current and electron flow

Answer 4

Conventional current: Positive to negative terminal

Electron flow: Negative to positive terminal

Question 5

Difference between conventional current and electron flow

Answer 5

Conventional current: Positive to negative terminal

Electron flow: Negative to positive terminal

Question 6

How to measure electric current

Answer 6

Ammeter, must be connected in series to circuit

Question 7

What is an electric circuit

Answer 7

An electric circuit is a complete or closed path through which charge can flow from one terminal of an electrical source to the other terminal

Question 8

What is electromotive force (e.m.f)

Answer 8

We define electromotive force as the work done by an electrical energy source in driving a unit charge around a complete circuit

Question 9

SI unit of e.m.f

Answer 9

Volt (V) or Joules per coulomb (J/C)

Question 10

Formula for e.m.f

Answer 10

E = W/Q

E - e.m.f (V)
W - work done (J)
Q - Charge (C)

Question 11

When cells are arranged in series, combined e.m.f (increases/decreases/remains the same)

Answer 11

Increases because electric charges gain electrical energy from each cell when they pass through them

Question 12

When cells are arranged in parallel, combined e.m.f (increases/decreases/remains the same)

Answer 12

Remains the same as the energy required to move electric charges through the load will be contributed equally by each cell

Question 13

What is potential difference

Answer 13

Potential difference across a component in a circuit is defined as work done to drive a unit charge through the component

Question 14

Formula for potential difference `

Answer 14

V = W/Q

V - Potential difference (V)
W - Work done (J)
Q - Charge (C)

Question 15

How to measure e.m.f and p.d.

Difference between e.m.f and p.d.

Answer 15

A voltmeter is used to measure the e.m.f of a dry cell and the p.d. across an electrical component. The voltmeter must be connected in parallel.

e.m.f is the voltage of all the batteries
p.d. is the voltage across objects i.e lamps

Question 16

What is resistance

Answer 16

Resistance is defined as the ratio of the potential difference across the resistor to the current flowing through it

Question 17

SI unit of resistance

Answer 17

Ohm (Omega)

Question 18

Formula for resistance

Answer 18

R = V/I

R - Resistance (Ohm)
V - Volt (V)
I - Ampere (A)

Question 19

What is Ohm’s Law

Answer 19

Ohm’s Law states that the current, flowing through a conductor is directly proportional to the potential difference across the conductor, provided that the physical conditions and temperature remains constant

Question 20

Ohmic conductors

Answer 20

Conductors that obey ohm’s law are called ohmic conductors. Resistance of an ohmic conductor can be obtained by finding gradient of V-I graph

Question 21

Non-Ohmic conductors

Answer 21

Conductors that do not obey ohm’s law are called non-ohmic conductors. Examples include filament bulb, thermistor and semi conductor diode

Question 22

Resistivity factors

Answer 22

-Temperature (T increase, R increase)

-Length (L)

-Cross sectional area (A)

-Material resistivity (P)

Question 23

Formula for resistivity

Answer 23

R = pL/A

R - Resistance (Ohm)
p - Material resistivity (Ohm)
L - Length (m)
A - Cross sectional area (m^2)