Current of Electricity (16) Flashcards
How can an electric current flow through a conductor
An electric current can flow through a conductor as it consists of free-moving electrons.
How can energy from the voltage source be transferred
Energy from the voltage source can be transferred by the flow of charges through a closed circuit but not an open circuit.
Define current
Rate of flow of electric charge
SI unit of electric charge
Coulomb (C)
SI unit of current
Ampere (A)
Relationship between Charge and protons/neutrons
Each electron/proton has the same amount of charge of 1.6 x 10 ^-19C. Thus 1 C of charge is approximately equal to 6.25 x 10 ^18 electrons/protons.
Formula for Current
I = Q/t
What is a conventional current
Conventional current is the flow of charges from the positive terminal of the battery to the negative terminal of the battery
What is an electron flow
Electron flow is the flow of electrons from the negative terminal of the battery to the positive terminal
Define Electromotive Force (e.m.f)
Electromotive force (e.m.f., ɛ or E) of an electrical source is the work done by the source in driving a unit charge around a complete circuit.
Define Potential difference (p.d.)
Potential difference (p.d.) across a component in a circuit is the work done to drive a unit charge through the component.
Formula of Work done/ W(joules), using V
V = work done/ Q
What is the relationship of V
The SI unit of e.m.f. and potential difference (p.d.) are measured in volt (V).
1 V is equivalent to 1 J/C.
Difference between emf and pd 1
e.m.f is the work done to move each unit charge through the circuits
P.d is the work done by each unit charge passing through the components
Difference between e.m.f and p.d 2
E.m.f is present even when no current is drawn through the source
P.d across any electrical component is 0 in the absence of current
What is used to measure e.m.f and p.d
E.m.f. and p.d. are measured by a Voltmeter connected in parallel across the two points to be measured.
Why does the electrical resistance of metals increase with temperature?
When electrons flow through a component, they collide with the ions of the components and with other electrons. These collisions resist the flow of the electrons.
Formula for resistance
R = V/I
SI unit for resistance
Ohm (Ω)
What are the factors affecting resistance of a conductor
o ρ - resistivity (Ωm) – depends on the material
o l - length (m)
o A - cross-sectional area (m 2 ) – depends on the thickness of the wire
Why does the resistance increase when the length of the wire is longer
The longer the cylinder, the more collisions the electrons will make with its atoms.
Hence, the resistance of the wire is directly proportional to the length
Why does the resistance increase when the cross-sectional area of the wire is larger
The larger the cross-sectional area of the cylinder, the greater the number of electrons that can flow through it.
Therefore, The resistance is inversely proportional to the area of the cylinder
Formula for R, using csa
Resistance = (Resistivity, p x length l ) / Cross-sectional area (A)
Define ohms law
Ohm’s Law states that: The current passing through a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions (such as temperature) are constant. (I V)
