Current and Charge Flashcards
What must there be for electrical current to flow?
a complete circuit and potential difference
What did physicists discover about conventional current?
it flows negative to positive
What is two quantities are the same in terms of electrons per second?
current and charge
What is the charge of an electron?
1.6 x 10^-19
What is charge in terms of electrons?
number of electrons x charge of one electron
In which particles is charge the fundamental property?
protons and electrons
Define charge carriers:
any charged particle that can move
What happens when charge carriers move?
transfer energy from the source to the component
Define current:
rate of flow of charge
What analogy is used for ‘electrons flowing in a circuit’?
balls flowing through a hollow pipe
What analogy is used for ‘the cell pushes electrons in the wire’?
an engine pushes balls in the pipe
What analogy is used for ‘when electrons go through the bulb or a resistor, they cause the wire to heat up’?
when the balls have to be squeezed through a thin section of the pipe they make the pipe hot
What analogy is used for ‘when the cell runs out the current stops flowing’?
when the engine runs out of fuel it will stop pushing the balls
What analogy is used for ‘measuring the current is counting the number of coulombs passing a certain point in the circuit each second’?
watching the number of balls passing a certain point of the pipe each second
What analogy is used for ‘the current is the same everywhere in the circuit’?
number of balls entering narrow strip= number of balls exiting narrow strip, speed of balls is constant
What analogy is used for ‘adding another cell will increase current’?
adding another motor will speed up the balls in the pipe
What analogy is used for ‘adding another resistor reduces current but it still remains the same across the circuit’?
adding an obstruction in the pipe will make the balls go slower
What analogy is used for ‘sum of current entering a point=sum of current leaving a point’?
number of balls entering a junction = number of balls leaving a junction
What did Milikan’s Oil Drop Experiment find?
calculated that the charge of an electron was about 1 x 10^-19 coulombs
What is the method of Milikan’s Oil Drop Experiment?
- oil mist produced by atomiser is sent through a plate of electrical condensor
- rate of fall measured through micrometer and can be controlled by the plate’s voltage
- X-Rays passed through the chamber ionise the air inside where the droplets acquire charge
What forces act on the oil drip in Milikan’s Oil Drop Experiment?
gravitational, electrostatic, viscous drag
What observations came from Milikan’s Oil Drop Experiment?
- charge on droplets is always a multiple of electron charge
- Q=ne
- charge of electron = 1.6 x 10^-19
- mass of electron is combination of Thompson and Milikan
Define potential difference:
energy supplied by the cell
1 Volt is…
when 1C of charge transfers 1J of energy potential difference is 1V
What is Kirchoff’s first law?
total current flowing into a point = total current flowing out a point
What is Kirchoff’s second law?
in a closed loop circuit potential difference across all components = 0
How are Kirchoff’s laws verified?
- in a series circuit more components = decreased potential difference because resistance increases
- resistance increases as current decreases as current remains the same across the circuit
Define number density:
number of free charge carriers per unit volume
Which materials have the highest number density?
conductors
Which materials have the lowest number density?
insulators
How does the cross sectional area impact mean drift velocity?
narrower wire gives greater drift velocity in order for current to remain the same
What is the relationship between mean drift velocity and cross sectional area?
inversely proportional
