P4 Electric Circuits Flashcards
What is a charged atom called?
Ion
Which subatomic particle actually moves?
Electrons
What charge do electrons have?
Negative
What does adding and removing the electrons do?
Adding electrons make the charge negative and removing makes the charge positive
how does some insulators get charged
they get rubbed by another insulator and they get charged
what happens when a polythene rod gets rubbed with a dry cloth
the dry cloth electrons move to the rod making it negatively charged
what happens when a perspex rod get rubbed with a dry cloth?
the electrons move from the perspex rod to the cloth and the rod becomes positively charged and they both have the equal charges
What is static electricity?
the stationary electric charge which is produced by friction which causes sparks, or the attraction of other small objects such as dust or hair.
What charges repel and attract
like charges(eg.+ and +) repel and opposite charges (eg-and+) attract
What does a cell do?
push electrons around a full circuit
What does the switch do?
allows the current to be switched on or off
What does a bulb do?
it is an indicator for when current passes through the signal and lights up
What do diodes do?
Diodes only let current in through one direction usually forward and LEDs emit light while doing so, they are used in the conversion from ac to dc.
What are ammeters and voltmeters?
ammeters measure current in amperes and voltmeters measure potential difference in volts.
What are resisitors?
A resistor is something that limits resistance, a variable resistor(rheostat) can change its resistance, light dependant resistors which lower resistance when light is increased, thermistors which lower resistors when temperature is high. A fuse breaks when a certain current is too high.
What is electric current?
An electric current is a flow of charged particles. In metal conductors the charged particles are free electrons. The electrons are free to move in one direction.
What is charge and current measured in?
Charge is measured in coulombs (C) and Current is measured in amperes(A)
What is the charge of one electron?
The charge of an electron is 1.6 x 10-19 C.
What is the formula for Current (I)
I=Q/t
Q=charge
t=time taken
What is potential difference?
Potential difference (or voltage) is a measure of energy, per unit of charge, transferred between two points in a circuit. A potential difference of 1 volt means that 1 joule of work is done per coulomb of charge
What is the formula for Voltage?(V,volts)
V=E/Q
e=work done, energy(joules, J)
What is the formula for resistance?
R=V/I
What is resistance measured in ?
Ohms(Ω)
How are ammeters and voltmeters fitted?
Ammeters in series and Voltmeters in parallel so they can read the pd across the component
Why is a wire an ohmic conductor?
Its resistance stays constant
What is the graph like for an ohmic conductor like a resistor?
A straight slanted line as it has constant resistance.
What is the graph like for an non ohmic resistor like a filament bulb
The graph is constant for a bit as the current increases resistance increases but then the temperature increases affecting the resistance forming the graph to curve away from the y.
What is ohms law?
For a fixed resistor, the potential difference is directly proportional to the current. Doubling the amount of energy into the resistor results in a current twice as fast running through the resistor. This relationship is called
Ohm’s Law
Why is a diode’s graph like that?
A
semiconductor
diode only allows current to flow in one direction. If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode’s resistance remains very large. Current will only flow if the diode is forward-biased. When forward-biased, the diode’s resistance is very large at low potential differences but at higher potential differences, the resistance quickly drops and current begins to flow.
What are the rules for a series circuit?
the same current passes through each component while the total p.d of the power supply is shared between the components so for current I1=I2=I3
While V=V1+V2+V3 AND RESISTANCE R=R1+R2+R3 resistance is shared.
What factor affect resistance?
length and thickness and type of the wire
temperature
How does temperature affect resistance?
As the temperature of the wire increases, the positive ions have more internal energy and vibrate with a greater displacement.
This increases the frequency of collisions between the electron and the positive ions.
Therefore the electron has to do more work and transfers more energy through the wire.
Resistance increases with temperature
What are electric field lines?
All charged objects have an
electric field
around them. This is similar to how magnets have a
magnetic field
. Electric
field lines
are not visible, but their effects are.
Any object with an electric charge will feel a force if it is in an electric field. It is not necessary for the charged objects to touch for the electric field to have an effect. Electric field lines are shown as:
leaving a positively charged object in all directions
entering a negatively charged object
closest where the field strength is greatest
What are better resistors insulators or conductors?
Insulators
What does reversing the pd across a resistor do?
reverse the current
The bigger the resistance the bigger the ____?
current
Rules for parallel circuits.
The total current is the sum of the currents through the seperate components
The pd is the same across all components
Resistance in a parallel circuit?
1/Rp=1/R1+1/R2+1/R3
