P4 Electricty Flashcards
What is current?
The rate of flow of charge.
(How many electrons (bits of charge) travel around a circuit in a given time)
What is potential difference?
The energy transferred to the electrons to make them travel around a circuit.
The push
What is resistance?
The opposition of a component to the flow of electric charge
What end do electrons flow from?
From the negative to the positive
What is conventional current?
When scientists thought the current of a circuit flowed from the positive to the negative poles of a battery
What is ohms law?
When the current flowing through a component is directly proportional to the potential difference across it
The temperature has to be constant
What is the difference between a series and a parallel circuit?
A series circuit has all components connected in one loop
A parallel circuit has more than one loop
What is the IV graph for a filament lamp?
A curve
As a potential difference increases more energy is transferred to the filament In the lamp. This causes particles to vibrate, increasing the resistance so the current does not flow as easily.
What is the IV graph for a diode?
Flat in One Direction, steep curve in the other
Diodes only allow current to pass through in One Direction
What is the current rule in a series circuit?
The current is the same at any point of the circuit
What is the potential difference rule in a series circuit?
Potential difference is split across each component
the potential difference of all the components is the same as the potential difference across the cell
What is the resistance rule in a series circuit?
Resistance is shared across each component
What is the current rule in a parallel circuit?
The current in the branches adds up to the total current leaving the cell
what does a potential difference of 1 volt mean?
1 Joule of energy is transferred for each Coulomb of charge moving through the circuit
what is the potential difference rule for parallel circuits?
the potential difference across each component is the same
what is a battery?
two or more cells connected together
what is charge measured in?
coulombs (C)
what is charge flow?
the total amount of charge that has flowed through a point in a circuit in a given time
what is the formula for charge flow?
Q = I x t
what is the equation for energy transferred?
E = Q x V
what does resistance tell us?
the potential difference required to drive a current through a component
what is the formula for resistance?
R = V / I
what is the unit of resistance?
the Ohm
what is an ohmic conductor?
where the potential difference is directly proportional to the current so the resistance is constant.
what effects the resistance of a fixed resistor?
the temperature
what are resistors used for?
to control the resistance across other components
what is the pattern for a I / V graph of a filament lamp?
the current is not directly proportional to the potential difference.
the curve is the same when the current is reversed
as the V increases, the I does not increase as much so the resistance is increasing.
why is the potential difference not directly proportional to the current with a filament lamp?
the filament gets hot which causes the resistance to increase
why does an increase in temperature increase resistance?
an increase in temperature causes the atoms to vibrate. this means the electrons in the current collide more with the atoms. more energy is then needed to push the current through
how does current flow through a diode?
in one direction only
this is because the diode has a really high resistance in the reverse direction
what does the arrow on the diode show?
the direction that the CONVENTIONAL current flows
what does the current potential difference graph for a diode look like?
there is no current in the reverse direction
in the forward direction, the current increases as the potential difference increases
what are diodes useful for?
controlling the flow of current in circuits
why are LEDs useful?
they are an energy efficient source of light
what is the rule of resistance in series?
resistors in series add together
this is because the current has to pass through the resistor in turn
what is the resistance rule for resistors in parallel?
the total resistance of two resistors is less than the resistance of the smallest individual resistor
why is the resistance rule of parallel circuits true?
there are more pathways for the current to take so more total current can flow through the circuit
what are the characteristics of an LDR?
resistance is high when it is dark
resistance is low in light
what are the uses of an LDR?
controlling things to do with light e.g.:
phone screens
lamps
what are the characteristics of a thermistor?
the resistance decreases if the temperature increases
what are the applications of thermistors?
thermostats (devices to detect temperature)
e.g.:
cooling fan in computers
incubator for premature babies
in the experiment with resistance, how can the zero error be rectified?
subtract the zero error from all the readings
what is a zero error?
a reading on an measuring instrument when the value should be zero
what reduces heating effects when carrying out an experiment?
use a low potential difference - this keeps the current low
only turn the current on when taking a reading
what is a variable resistor used for in an investigation?
it is adjusted to get new readings of the ammeter and voltmeter
why is the position of the battery switched around? (in an investigation)
to get negative readings on the ammeter and voltmeter
why is an extra resistor added in the circuit when investigating a diode?
diodes get easily damaged by a high current
the extra resistor will keep the current low to protect the diode
why do you need a milliammeter when investigating a diode?
the current will be kept low to protect the diode. this means the ammeter needs to be sensitive
why can insulators not conduct electricity?
electrons cannot move through them
what happens when you rub two insulators together?
electrons are transferred from one insulator to another
this causes the insulators to have equal opposite charges
what happens if electrostatic charge builds up?
it can cause a spark
which charges attract?
opposite charges attract
what is a non-contact force?
where objects are exerting a force on one another but they are not touching
which charges repel?
like charges repel
how must field lines be draw?
perpendicular to the surface of the object
what do the arrows on field lines show?
the direction of the force when a positively charged object comes nearby
what happens if charged objects are brought closer together?
they experience a stronger force
what is an electric field?
the area around a charged object that exerts a force on all other charged objects
