p3 - electricity (from PMT) Flashcards
what can happen when insulating materials are rubbed together
they can become statically electrically charged
define charging
the addition or removal of electrons from a material
how can charge be detected?
using a gold leaf electroscope; the gold leaf is repelled by positive charge
what happens when two electrically charge objects are brought close together?
they exert a force on each other
define an electric field
a region in which a charge object will experience a non-contact electrical force
where can electric fields be found?
surrounding any charged object
describe the electric field around a charged particle
-strongest closest to the object
-decreases in strength as you move away from the object
in situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?
any surfaces that are rubbing against each other should be earthed to allow the materials to discharge
define electric current
the flow of electrical charge
define a series circuit
a series circuit is one in which the same charge passes through all components, so the current through each component is the same
define a parallel circuit
a circuit in which the charge is split between branches
describe ohm’s law
current and potential difference are directly proportional, given that resistance and temperature remain constant
list 4 components for which resistance is not constant as current changes
-lamps
-diodes
-thermistors
-LDRs
what happens to the resistance of a filament lamp as the temperature increases + why?
-resistance increases
-ions in metal have more energy, so vibrate more, more collisions w electrons, greater resistance
what is difference about current flow through a diode?
-current only flows in one direction
-resistance is very high in the other direction, preventing current flow
state what happens to the resistance of a thermistor as temperature increases
resistance of the thermistor decreases
give 2 examples of when a thermistor may be used
-in a thermostat to turn a heater on below a certain temperature
-in a freezer to turn on a cooler when the temperature becomes too high
state what happens to the resistance of a LDR as light intensity decreases
-LDR’s resistance increases
give an application for a LDR
street lamps - when light levels become low enough, the light gains sufficient current to turn on
what are the two ways that a component can be connected in a circuit?
-series
-parallel
how does the potential difference across two components vary when connected in series and parallel?
series: total p.d shared between each component
parallel: p.d across each component is the same
how should a voltmeter be connected in a circuit?
in parallel to the component that you are measuring the potential difference for
how should an ammeter be connected in a circuit?
in series with the branch you are measuring the current for
