Current Electricity Flashcards
current
the rate of flow of charge
what is current measured in?
A
what is the formula for current
Q=I/\t
conventional current?
flows from the positive pole of the cell around the circuit to the negative pole of the cell.
electron current
flows from the negative pole of the cell around the circuit to the positive pole of the cell.
what is potential difference?
is the work done per unit positive charge
true or false: Current will flow between 2 points in a circuit if there is no potential difference between the 2 points.
false
Current will NOT flow between 2 points in a circuit if there is no potential difference between the 2 points.
true or false: In a cell, charge move from one point of high potential to a point of low potential, and electrical energy changes to heat, light, and other energy forms
In the circuit
true or false: In the circuit, charge move from one point of low potential to a point of high potential, and chemical energy is converted to electrical energy. The increase in electric potential provided by a cell is called an emf
in a cell
what is potential difference measured in ?
Volts
the formula for potential difference
V=W/Q
WHAT IS RESISTANCE
a material’s opposition to the flow of electric current
formula for resistance
R=V/I
true or false: When components of a circuit are connected in series there is only one pathway so the same current must flow through all the series connections
true
cells in series
The positive pole of one cell is connected to the negative pole of the next cell. The total emf is the sum of the individual emf’s
resistors in series
=The current is the same for all resistors
=The potential difference across the series connection is equal to the sum of the individual values.
=The total resistance is equal to the sum of all the separate resistances.
=A series connection is a potential divider. The potential difference divides in the same ratio as the resistors.
ammeters in series
measure the current through a resistor and must be connected in SERIES with the resistor. An ammeter has a very low resistance
connecting in series
When components are connected in series there is only one pathway so the same current must flow through all the series connections.
connecting in parallel
there is more than one pathway between 2 points. This means that different pathways will have different current values. There can only be one value for the potential difference between the 2 points.
cells in parallel
All the positive poles are connected to one point and all the negative poles are connected to another point. The emf is the same as the emf of a single cell.
resistors in parallel
=the potential difference across all branches of a parallel circuit
=The total current in a parallel circuit is equal to the sum of the currents in the separate branches.
=In a parallel circuit the total resistance
=a parallel connection is a potential divider. The current divides in the inverse ratio to the resistors.
the formula for resistance in a parallel circuit
i/R=1/r1+1/r2+1/r3 or
r1r2/r1+r2(2 resistors)
Voltmeters
measure the potential difference ACROSS a resistor and must be connected in parallel with the resistor. Voltmeters have high resistance so only a small current will flow through them.
state Ohm’s law
The current through a given conductor is directly proportional to the potential difference between its ends provided the temperature remains constant.
good and bad conductors of electricity
metals such as copper, silver, and gold offer low resistance to the flow of charge. Metals such as tungsten, nickel, and chrome offer high resistance to the flow of charge.
which conductor does not obey ohm’s law
a non-ohmic conductor
diodes, transistors, and semi-conductors
will only allow the flow of charge at certain voltages and in certain directions. They are ohmic conductors. Light bulbs are non-ohmic conductors because their resistance changes as they get hot.
discuss energy(w)
used by component in a circuit depends on the potential difference across the component (V), the current that flows through it(I), and the length of time for which the current flows(delta t). Energy is measured in Joules
discuss power(P)
used by a component in a circuit is the energy used per second. Power is measured in Watts.
the 2 power equations
P=I^2R
P=V^2/R
the 2 energy equations
W=IV^2/R X delta(t)
switches in circuits
control the way in which meters and resistors are connected in a circuit. When a switch is switched on or off this will change the resistance, the current, and the voltage at different points in the circuit.
Luigi Galvani (1737-1798)
a proffessor of anotomy at bologna.He discovered animal electricity.
Alessandro Volta(1745-1827)
was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the discoverer of methane
André-Marie Ampère(1757-1836)
was a French physicist, mathematician and lay catholic who was one of the founders of the science of classical electromagnetism, which he referred to as “electrodynamics”. He is also the inventor of numerous applications, such as the solenoid and the electrical telegraph
Georg Simon(1789-1854)
ohm’s law
James Prescott Joule
1818-1889
as an English physicist, mathematician and brewer, born in Salford, Lancashire. Joule studied the nature of heat, and discovered its relationship to mechanical work. This led to the law of conservation of energy, which in turn led to the development of the first law of thermodynamics.
Thomas Alva Edison(1846-1931)
was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures.
speak on AMMETERS
=current strength
=series
=current flows through it
=low resistance
speak on VOLTMETERS
=potential difference over points
=parallel
=current cannot flow through it
=High resistance
