Ch 13 Electric Charge and Current of Electricity# Flashcards
What types of charges are there in static electricity?
positive and negative charges.
What is the SI unit for charges?
coulomb (C)
What is the difference between a neutral object and a negatively charged object?
Think in terms of no. of protons and electrons.
A neutral object contains equal number of protons and electrons.
A negatively charged object contains more electrons than protons.
The same can be compared for a positively charged object.
Define the law of electrostatic.
Like charges repel.
Unlike charges attract.
What is an electric field?
A region where an electric charge experience an electric force.
Define current.
Current is the rate of flow of electric charge.
What is the SI unit of current?
Ampere (A)
What is the instrument used to measure current in a circuit?
Ammeter / digital multi-meter
How should the ammeter be connected in a circuit?
connected in series
What is the name given to this type of current flow?
Elecron flow
Take note of how the current’s direction with respect to the termials of the battery.
What is the name given to this type of current flow?
Conventional current
Take note of how the current’s direction with respect to the termials of the battery.
What is the relationship between I, Q and t?
(in other words the formula)
[Please recall what I, Q and t represents]
Q = It
Define electromotive force (e.m.f.).
Electromotive force (e.m.f.) is the amount of work done by a source (e.g. battery, cell) 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 of charge through the component.
What is the SI unit of electromotive force (e.m.f.)?
Volt (V)
What is the SI unit of potential difference (p.d)?
Volt (V)
What is the instrument used to measure voltage across a component in a circuit?
voltmeter / digital multi-meter
How should the voltmeter be connected in a circuit?
connected in parallel to the component
What is the relationship between V, W and Q?
(in other words the formula)
[Please recall what V, W and Q represents]
W = VQ
Define resistance.
Resistance of a component is the ratio of voltage to current in a component.
What is the relationship between R, V and I?
(in other words the formula)
[Please recall what R, V and I represents]
R = V / I
What is the SI unit of resistance?
ohm (Ω)
What are the factors that affect the resistance of a wire?
[There are 4 factors.]
1) length of wire (l)
2) cross-sectional area of wire (A)
3) resistivity of the material (ρ)
4) temperature of wire
State how the length of wire affects the resistance.
The longer the wire, the larger the resistance.
State how the thickness of wire affects the resistance.
thickness also means cross-sectional area of wire
The thicker the wire, the lower the resistance.
The thinner the wire, the higher the resistance.
State how temperature of a wire affects its resistance.
The higher the temperature, the larger the resistance.
Define Ohm’s Law.
Ohm’s law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remains constant.
Explain why the filament lamp does not obey Ohm’s law.
As current flows through the filament lamp, it heats up and increases the resistance of the filament lamp.
What are the 2 factors on a VI graph that shows an electrical component obeys Ohm’s law?
(i.e. what are the 2 things to look out for in a VI graph?
1) The graph must be a straight line.
2) The line must pass through the origin.
