P4.2 - current/charge/volatge/resistance Flashcards
electric current
-flow of charge
-more electron flow per sec = bigger current
size of current =
rate of flow of charge
or charge per sec
electric charge unit
coulombs C
Current unit
amperes A
1 amp = how many c
1C per sec
equation for charge flow, current, time
charge = current x time
conventional flow
-positive to negative
electron flow
-negative to positive
Components of a circuit: cell
-pushes electrons around circuit
Components of a circuit: battery
2 or more cells
Components of a circuit: switch
-enables current to turned on/off
Components of a circuit: lamp
-emits light when current passes through
Components of a circuit: diode
allows current through one direction only
Components of a circuit: LED (light-emitting diode)
emits light when current passes the right way
Components of a circuit: ammeter
measures current
Components of a circuit: fixed resistor
limits current in a circuit
Components of a circuit: variable resistor
allows current to be varied
Components of a circuit: fuse
melts and breaks circuit if current it too big
-safety mechanism
Components of a circuit: heater
-transfer energy from current to heat surroundings
Components of a circuit: voltmeter
measures P.D / voltage
Has to be parallel to the thing it’s measuring
potential difference
-energy transferred to component that passes through it
equation involving pd/energy/charge
P.D = energy transferred/charge
resistance
-electrons passing through components have to push their way through lots of vibrating atoms
=resistance
equation involving resistance/voltage/current
R=V/I
unit for resistance
ohms
larger resistance .. =
lower current
ohms’ law states
-current passing through the resistor at a constant temp
-is directly proportional to PD of resistor
ohmic conductor
resistance stays constant as current changes
-when temp is constant = obeys ohms law
reversing pd across resistor =
reverses current
non ohmic conductor eg
filament lamp
diode
non ohmic conductor - filament lamp
-resistance isn’t constant
-charge depends on current
-not proportional
-higher current = more resistance as temp increases
non ohmic conductor - diode
-low resistance in forward direction
-high resistance in the reverse direction
ohmic conductor IV graph
-straight line
-goes through origin
- directly proportional
non ohmic conductor - filament lamp
-curved line
-not proportional
non ohmic conductor - diode
-forward direction line curves towards y axis
-reverse direction current = 0
thermistors
temp dependent resistor
-resistance decreases if temp increases
LED
-decreases resistance if the light intensity increases
series circuits
consist of one loop of wire
current in series circuits
-same current through each component
series circuits - PD
-total pd is shared between components
series circuits - resistance
-total R = R1+R2
Parallel circuits
consists of 2 or more loops of wire
Parallel circuits - pd
-pd is same across all components
Parallel circuits - current
-total current = sum of current through components on each loop
Parallel circuits - resistance
-total resistance is less than the resistance of the smallest resistor
-1/R1 + 1/R2 = Rt
Light dependent resister or LDR
High light intensity - low resistance
