p3 - electricity (from PMT)

Question 1

what can happen when insulating materials are rubbed together

Answer 1

they can become statically electrically charged

Question 2

define charging

Answer 2

the addition or removal of electrons from a material

Question 3

how can charge be detected?

Answer 3

using a gold leaf electroscope; the gold leaf is repelled by positive charge

Question 4

what happens when two electrically charge objects are brought close together?

Answer 4

they exert a force on each other

Question 5

define an electric field

Answer 5

a region in which a charge object will experience a non-contact electrical force

Question 6

where can electric fields be found?

Answer 6

surrounding any charged object

Question 7

describe the electric field around a charged particle

Answer 7

-strongest closest to the object
-decreases in strength as you move away from the object

Question 8

in situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?

Answer 8

any surfaces that are rubbing against each other should be earthed to allow the materials to discharge

Question 9

define electric current

Answer 9

the flow of electrical charge

Question 10

define a series circuit

Answer 10

a series circuit is one in which the same charge passes through all components, so the current through each component is the same

Question 11

define a parallel circuit

Answer 11

a circuit in which the charge is split between branches

Question 12

describe ohm’s law

Answer 12

current and potential difference are directly proportional, given that resistance and temperature remain constant

Question 13

list 4 components for which resistance is not constant as current changes

Answer 13

-lamps
-diodes
-thermistors
-LDRs

Question 14

what happens to the resistance of a filament lamp as the temperature increases + why?

Answer 14

-resistance increases
-ions in metal have more energy, so vibrate more, more collisions w electrons, greater resistance

Question 15

what is difference about current flow through a diode?

Answer 15

-current only flows in one direction
-resistance is very high in the other direction, preventing current flow

Question 16

state what happens to the resistance of a thermistor as temperature increases

Answer 16

resistance of the thermistor decreases

Question 17

give 2 examples of when a thermistor may be used

Answer 17

-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

Question 18

state what happens to the resistance of a LDR as light intensity decreases

Answer 18

-LDR’s resistance increases

Question 19

give an application for a LDR

Answer 19

street lamps - when light levels become low enough, the light gains sufficient current to turn on

Question 20

what are the two ways that a component can be connected in a circuit?

Answer 20

-series
-parallel

Question 21

how does the potential difference across two components vary when connected in series and parallel?

Answer 21

series: total p.d shared between each component
parallel: p.d across each component is the same

Question 22

how should a voltmeter be connected in a circuit?

Answer 22

in parallel to the component that you are measuring the potential difference for

Question 23

how should an ammeter be connected in a circuit?

Answer 23

in series with the branch you are measuring the current for