Current of electricity Flashcards
What is an electric current
Electric current, I, is defined as the rate of flow of electric charge through a given cross-section of conductor
SI unit of current
Ampere (A)
Formula for current
I = Q/t
I - Electric current (A)
Q - Charge (C)
t - Time (s)
Difference between conventional current and electron flow
Conventional current: Positive to negative terminal
Electron flow: Negative to positive terminal
Difference between conventional current and electron flow
Conventional current: Positive to negative terminal
Electron flow: Negative to positive terminal
How to measure electric current
Ammeter, must be connected in series to circuit
What is an electric circuit
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
What is electromotive force (e.m.f)
We define electromotive force as the work done by an electrical energy source in driving a unit charge around a complete circuit
SI unit of e.m.f
Volt (V) or Joules per coulomb (J/C)
Formula for e.m.f
E = W/Q
E - e.m.f (V)
W - work done (J)
Q - Charge (C)
When cells are arranged in series, combined e.m.f (increases/decreases/remains the same)
Increases because electric charges gain electrical energy from each cell when they pass through them
When cells are arranged in parallel, combined e.m.f (increases/decreases/remains the same)
Remains the same as the energy required to move electric charges through the load will be contributed equally by each cell
What is potential difference
Potential difference across a component in a circuit is defined as work done to drive a unit charge through the component
Formula for potential difference `
V = W/Q
V - Potential difference (V)
W - Work done (J)
Q - Charge (C)
How to measure e.m.f and p.d.
Difference between e.m.f and p.d.
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
What is resistance
Resistance is defined as the ratio of the potential difference across the resistor to the current flowing through it
SI unit of resistance
Ohm (Omega)
Formula for resistance
R = V/I
R - Resistance (Ohm)
V - Volt (V)
I - Ampere (A)
What is Ohm’s Law
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
Ohmic conductors
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
Non-Ohmic conductors
Conductors that do not obey ohm’s law are called non-ohmic conductors. Examples include filament bulb, thermistor and semi conductor diode
Resistivity factors
-Temperature (T increase, R increase)
-Length (L)
-Cross sectional area (A)
-Material resistivity (P)
Formula for resistivity
R = pL/A
R - Resistance (Ohm)
p - Material resistivity (Ohm)
L - Length (m)
A - Cross sectional area (m^2)
