P4 - Electric circuits Flashcards
What does a charged object do to the space around it?
creates an electric field
eg an electricity pylon’s wire will create an electric field around it
How can an uncharged object become positively charged?
-negatively charged electrons are transferred
-from the neutral object
Specimen 2018, Q6.1 [3]
How do you draw an electric field diagram?
field lines always point away from a positive source and towards a negative source
What happens to certain insulating materials when they are rubbed together?
-electrons are rubbed off from one onto the other
-they become of equal and opposite electric charge
How do charged objects interact?
-interacts through a non-contact electrostatic force
-like charges repel
-opposite charges attract
How does a Van de Graaff generator work?
-belt inside the insulating tower rubs electrons off onto the inside of the metal sphere, which builds up a negative charge as it can’t discharge to the ground
-when a conducting object comes close to the sphere, the electrons discharge and earth, seen as a spark
If you are wearing rubber boots, the electrons won’t discharge into you
Give the symbol for a diode and an LED:
usually both are meant to have circles around it
Draw the symbol for a standard and variable resistor:
What is the symbol for a fuse?
RP3 - How can you investigate how the resistance of a wire changes with length?
-set up circuit
-tape uninsulated wire to metre rule, and attach a fixed crocodile clip to one end, and the one to be moved at a certain distance along the wire
-record I from ammeter and V from voltmeter, and calculate R for each interval
-plot a graph of R vs length of wire
RP3 - How can you find how resistance changes between series and parallel circuits?
-make circuit with 2 equal resistors in series, with ammeter and voltmeter (around both resistors), and calculate total resistance
-repeat but put each resistor in parallel in its own branch, and ammeter in series (not in a branch) and a voltmeter, calculate resistance again (should be a lower value)
What is an ohmic conductor? Draw its IV graph:
-follows Ohm’s law
-a conductor where the current flowing through it is directly proportional to the PD across it (at constant temp.)
-and the resistance is constant
Give some examples of some non-ohmic conductors, and draw their IV graph:
-diodes (doesn’t have the same graph as the 3 below)
-lamps
-thermistors
-LDRs
Why aren’t some conductors ohmic?
-their temperature increases due to the increased current
-resistance increases (particles vibrate more and electrons bump into them)
How does current flow through a diode? Draw its IV graph:
-flows in one direction only (in the direction of the arrow)
-very high resistance in other direction
What is a thermistor? Give its symbol, and a use for it:
-resistance decreases as temperature increases
-thermostats
What is an LDR? Give its symbol, and its uses:
-resistance decreases as light intensity increases
-switching lights on when it gets dark
RP4 - How can you investigate the IV characteristics of certain components?
-set up circuit
-record I from ammeter and V from voltmeter
-alter resistance on variable resistor in regular increments
-repeat to get a range of readings
-flip battery to get negative readings
-plot an IV graph for that component
-repeat by replacing resistor for diode/lamp
Describe the IV characteristics of a series and a parallel circuit:
series - current constant, PD distributed between components depending on the their resistance
parallel - PD constant, current distributed between different branches depending on the total resistance of that branch
What happens when you add resistors in another branch into a parallel circuit?
-current has more paths to go through
-total resistance decreases
You can represent this mathematically using the equation for the total resistance in parallel
Which lamp will be brighter at any potential difference and why?
-A has a higher current than lamp B at any PD
-therefore A has a higher power output (P=IV) than B, and will be brighter
