P- 2- Electricity Flashcards
1
Q
- What is current
A
- The flow of Electrical charge
- Measured in Amps
2
Q
_ What is needed to make electrical charge flow
A
- Complete circuit
- Potential difference
3
Q
- What is potential difference
A
- Force that pushes the charge- volt
4
Q
- What is the distribution of current around a full circuit
A
- Even at every point
5
Q
- What is resistance
A
- Anything that slows the flow down
- Measured in ohmes
6
Q
- What does current depend own
A
- Potential difference and resistance
7
Q
What does total charge depend on
A
- Current and time
- Q= It
- Charge flow = current x time
8
Q
What are the symbols of cell and resistor
A
Cell - —-±||—–
Resistor ——| |——–
9
Q
What are the symbols for battery and variable resistor
A
Battery ——±| |——-±| |——-
Variable resistor —|_/|
10
Q
What are the symbol for switch open and ammeter
A
Switch open- ___./ ._____
Ammeter - A - in circle
11
Q
- What are the symbols for voltmeter and switch closed
A
- Switch closed- __.__.___
- Voltmeter- —V—- In circle
12
Q
What are the symbols for filament lamp and diode
A
Filament - —-x—- - In circle
Diode- —–|>|— In circle
13
Q
What re the symbols for fuse and LDR
A
- Fuse - ——|——-|——-
LDR- —–|___|——–
14
Q
- Wat are the symbol;s for LED and thermistor
A
// - LED- ---|>|-----
Thermistor—-|_/___|——-
_/
15
Q
- What is the formal for potential difference and current
A
- Potential difference = Current x resistance
16
Q
- How can you investigate resistance factors
A
- Wire length
- Attach crocodile clip to wire at 0cm
- Attach second crocodile clip to wire - writer down length between
- Close switch and mature current and PD
- Open switch and move along a fixed measurement and retest- repeat
- Use measurement and calculate resistance using formula
- Polt graph- should be directly proportionate
- IF not may be a systematic error e.g first clip not at 0
17
Q
- What its the ammeter
A
- Measures current in amps flowing through a wore
- Placed in series with what you are doing
18
Q
- What is a voltmeter
A
- Potential difference across test wire
- Must always be placed in parallel around what you are testing - not around any other
19
Q
- What happens in resonance of Ohomic conductors
A
- It does not change with current
- e.g wire or resistor
- at constan temp current flowing is directly proportionate t potential difference
20
Q
- What happens in appliances where resistance changes
A
- e.g diode and filament lam
- Filament- - transfers energy to thermal store - heats up - resistance increases with temperature - as current increases so does resistance
- Diode- Depends on direction of current - very high resistance if reversed
21
Q
what are I- v Characteristics
A
- Refers to a graph which shows how current flowing through changes as potential difference increases
- Linear components I-v are straight ;owed-
-Non linear- Curved
-
22
Q
- How can you test for the I-v Characteristics
A
- Set up test circuit with variable resistor, component, ammeter, voltmeter, component and battery
- Begin to vary variable resistor- alters current flowing an potential difference
- Take several pairs of readings from ammeter and voltmeter- to see how potential difference varies as current varied- repeat and get average
- Swap over wires so its reversed
- Plot a graph of current against voltage
23
Q
- What do I-v Characteristic s look like for , ohmic conductors, filament lamps and diodes
A
- Ohomic- Straight- linear
- Filament- Curved going both under and over
- Diode- Only appears in positive and steep
24
Q
What is LDR
A
- Light dependant resistor
- Dependent on intensity of light
- Bright light causes resistance to fall
- Darkness - resistance is highest
- e.g Automatic night lights and burglar detectors
25
-What is a thermistor
- Temperature dependant resistor
- Hot conditions cause resistance to drop
- Cool conditions cause increase in resistance
- Good tematyre sectors e.g car engines
26
What can sensing circuits be used for and how
- Turn on or increase power to components depending on conditions
- Fixed resistor will always have the same potential difference as there connected in parallel
- PD is shared between thermistor and loop according to resistance - bigger resistance means more PD
- As it become shorter Resistance of thermistor decreases- more PD to fan- Fan goes faster when its hotter
27
What are sires circuits
- Different comments are connected in a line end to end, between =ve and -ve of power supply - except voltmeters
- If you remove or disconnect one component the circuit is broken- not very practical
- Measure quantities and test components
28
- What are the characteristics of a sires circuit
- Potential different is shared- always add unto source
- Current is equal everywhere - size of current is determined by total PD of cells and total resistance of circuits - I = V//R
- Resistance adds up- total resistance adds together to find ass- as they have to share PD- Total current is reduced when resistor is added - bigger resistance is the bigger its share
29
- Give a worked example for finding current passing through as 20 volt circuit with one 2 Ohme resistor and a 3 homes resistor
- Resistance total + 5 Ohmes
- I= V= R
20//5
+ 4A
30
- What are parallel circuits
- Each component is separate;y connected to +VE and -VE of Supply- except ammeters
- If you remove or add one nothing changes
- Most things connected this way
31
- What are the characteristics of a parallel circuit
- All components get full source of PD- PD same across all components- means all bulls are same brightness
- Current is shared- Total current = total of current in all other components
- Junctions where current splits or junctions- HAs to be equal to current leaving
- IF identical components are connected they all have the same current
- Adding a resistor reduces total resistance- IF you have two their total resistance is less than resistance of smallest of two resistor
32
-How do you investigate the effect of adding resistors in Siries circuits
- Need four identical resistors
- Build circuit using one resistor- make not of PD
- Measure current- Calculate resistance to measure current
- Add another resistor and measure current
- Repeat
- Plot
- Should follow linear positive
33
- What can you do to investigate effect off restores in Parallel circuits
- Set up parallel circuit
- Need four identical resistors
- Measure total current and calculate current using resistance- V being PD of battery
- Add restore sea repeat
- Plot graph
- Should follow non direct proportional negative lines- that follows the diminishing returns
34
- What is alternating current
- Current is constantly changing directions
_ Produced by alternating voltages- positive and negative is costly switching
- Uk mains ac supply is 230 - 50 HZ- or cycles per seconds
35
- What is direct current
- Current laws flowing in same direction
- Created by direct voltage
- Batteries
36
- How are most cables in plugs structured
- 3 sperate wires - Core of copper and coloured plastic stating
- Colour of insulation on each cable shows purpose - always sa,e
37
- What are the three parts of the club and there function
- Natural wire - Blue- Complete circuit and carries away current- Normally flows in through live and out though neutral
- Live- Brown - Provides alternating potential difference- 230v- flows into
- Earth wire- green and yellow- Protecting wire and safety- stops appliance casing from becoming live- no current usually
38
- How can live wire give a shock
- Large potential differences produced across body and current flows through you
- Causes shock that may kill you
- Even if its off - there is still POD and a risk of a shock- Body would provide link and current flows through you
- Any connection between li e and earth can be dangerous. Link may create path top earth and huge current would flow- causing a fire
39
- How is energy transferred
- From cells and other courts
- Moving charge transfers energy as charge works against resistance
- Electrical appliances are designed to transfer energy to components
40
- Give tow examples of how appliances
- Kettles transfer electrical from mains into thermal to heating element
- handheld fan- Electric from battery into kinetic
- Not all useful- higher current causes higher amounts of thermal energy transfer
41
- What does energy transferred depend on
- Power
| - Toal energy by an appliance depends how long the appliance is on for and its oiler
42
- What is power
- Is energy that it transferred per second
| - More energy means more power
43
- How can you work out energy transferred
- Energy transferred = Power x time
E=Pt
44
What is a power rating
- labelled with maximum safe oiler they can operate at
- Maximum amount of energy transfer between stores per second
- Helps customer choose- lower power ratings- less electricity is uses- cheaper
- Higher power rating does not mean more energy is transferred - fails to address usefulness of energy transferred
45
- What is potential difference
- Energy transferred per charged passed
- When electrical charge goes through a change in potential difference then energy is transferred
- Energy supplied to charge at power source to raise it through a potential
- The charge gives up this energy where it falls through any potential drop in components
-
46
- What is the formula for potential difference
- Energy transferred = Charge flow x potential difference
E= QV
-
47
- What does a battery with a lager PD mean
- Will supply more energy for every coulomb of charge which flows around it, because charge is raised higher at the start
48
- How does power depend in current and potential difference
- Power = Potential difference x current
- if you don't know potential difference you can rearrange to get P= I2R
- R- resistance
49
- How is electrify distributed
- Via the national grid
- - giant system of cables and transformers that covers Uk and connects power stations to consumers
- National grid transferred electrical power from power stations to demand
50
- What does production have to meet
- Demand
- usage changes throughout day- power stations have to keep up with this demand
- Can predict when demand is highest- e.g time of day or big event
- Many run far below maximum power output so they can always meet high demand
- Lots of power stations that are smaller can open up fast if in need
51
- What does the national grid use
- High potential difference and low current
- To transmit he amount of power you need either high
- Problem with high current is you lose loaf of energy to thermal loss
0 Most chapter to boost PD to 400,000 and keep current low
-- mAke it very efficient
52
- How is potential difference impacted by transformers
- To get to such a high PD requires transformers as well and big pylons and huge insulators - but its still cheaper
- The transformer shave to step the potential difference up at one end and down to a usable level at another
53
- How is potential difference increased and reduced
- PD increased using step up transformer
| - Reduced using step down transformer
