Electricity Flashcards
Recall the symbol for current
I
Recall the symbol for charge
Q
Recall the symbol for energy
E
Recall the symbol for resistance
R
Recall the symbol for voltage
V
Recall the symbol for power
P
What is current measured in?
Amperes/amps, A
What is charge measured in?
Coulombs, C
What is energy measured in?
Joules, J
What is resistance measured in?
Ohms, Ω
What is voltage measured in?
Volts, V
What is power measured in?
Watts, W
Current is a measure of?
Rate of flow of charge
Voltage is?
The energy transferred per coulomb of charge (one volt equals one joule per coulomb)
What is electric current in a wire?
A flow of electrons
Recall the formula involving charge, current and time and how it is useful
Charge = Current x time
Q = I x t
To determine how much charge has passed a point in a circuit in a given time
Give a common conductor material
Metals
Give a common insulator material
Plastic
Understand and identify five hazards associated with electricity
Frayed cables Long cables Damaged plugs Water around sockets Pushing metal objects into plug sockets
What does the current in a series circuit depend on?
The applied voltage and resistance of the components (bigger voltage = larger current, but large resistance, resists flow of current = smaller current
Recall equation including voltage, current and resistance
Voltage = Current x resistance V = I x R
What is the current like in a series circuit?
Current is the same at every point
What is the current like in a parallel circuit?
Current is ‘split’ between the ‘arms’ of the circuit (current is conserved at junctions)
What is voltage like in a series circuit?
Voltage is ‘split’ between each of the components e.g.. bulbs
What is voltage like in a parallel circuit?
Voltage is the same across each component eg. bulb
Describe how current varies with voltage for a fixed resistor
straight diagonal line that goes through zero
Describe how current in a wire or filament lamp transfers energy to it, and causes it to heat up
Larger current = electrons flow faster
Sometimes electrons collide with the structure of metal, pass on kinetic energy (wire gets hot)
Ions vibrate more, electrons find it harder to flow through structure
Harder to flow = bigger resistance
As current increases, resistance increases
Explain what the gradient of a graph of voltage against current gives us
The resistance
Steep = high resistance
Shallow = low resistance
and other way round for graph of current against voltage
What can lamps and LEDs be used to indicate?
The presence of current in a circuit
Explain why a parallel circuit is more appropriate for different applications
Can control each component separately
If one breaks, others still work
Explain why a series circuit is more appropriate for different applications
Can control all components simultaneously
Explain how fuses work
Made of thin wire
If too much current passes through, fuse melts
This breaks the circuit and prevents overheating or a fire
Explain how earthing works
Earth wire is a low resistance safety wire that is attached to Amy exposed metal part on the appliance
If fault in device and live wire touches outside metal part
Earth wire low resistance so large current surges through it
Surge of current causes fuse to melt
Circuit broken
Nobody electrocuted
Only required for appliances with metal casing
Double insulators don’t require?
An earth connection
What are the advantages of using a circuit breaker over a fuse?
Can be reset
Acts faster than a fuse (doesn’t have to melt)
Recall the equation linking power, current and voltage
Power = current x voltage P = I x V
Recall equation linking energy, charge and voltage
Energy = charge x voltage E = Q x V
Recall equation linking energy, current, voltage and time
Energy = current x voltage x time E = I x V x t
Whats direct current?
Current flows in one direction continuously
eg. batteries
What is alternating current?
Current continuously switches direction
eg. Mains electric, plugs
How are positive and negative electrostatic charges produced on materials?
By the loss and gain of electrons when surfaces rub together (through friction)
Describe how two objects with opposite charges will attract?
Positively charged rod with fewer electrons and negatively charged rod with more electrons attract each other due to the electrostatic force
Describe how two objects with alike charges will repel?
Two rods either both positively or negatively charged will repel each other due to the electrostatic force
Describe how you could test the static charge on different objects using another charged object to attract/repel them
Hang plastic ball on nylon thread, ball has metal coating, not charged
Rub strip of polythene with cloth, strip becomes negatively charged
Brings strip close to the ball but doesn’t touch it
Ball moves toward strip
Why?
Brings an overall negatively charged rod near it
Electrons are pushed to far side (repelled)
The closer side is now positively charged
The farer side is now negatively charged
Because positively charged side is nearer the rod it attracts, while the negative side stays negative
The positive side is more attracted than the negative is repelled
Describe a simple electrostatic phenomena
When electrons ‘arc’ from a charged surface to a neutral/earthed surface
Electrons want to disperse so jump from negatively charged surface to neutral surface
Explain why when a charged object is brought near a neutral object, it always attracts?
Neutral object has equal positive and negative charge, electrons evenly spread over surface
Charged objects have fewer or more electrons
The two objects want to even out number of electrons and so are attracted
Explain some of the dangers of electrostatic charges
e.g. When refuelling tankers or airplanes, first and earth wire is connected
This allows any charge that has built up to flow (discharge) as a (brief) flow of current
This stops electrons jumping (arcing) from airplane to the person refuelling/hose and therefore prevent a spark that causes a fire
Explain some of the uses of electrostatic charges
Inkjet printer - nozzle sprays ink that is statically charged Plates either side and positively or negatively charged to direct the 'jet' of ink Photocopier - All of drum is charged as it passes a point Image to be copied is flashed at drum Special metal (selenium) loses charge on white parts, keeps it on dark parts Photocopier drops toner onto drum which sticks to charged parts only As paper rolls under drum the toner is pressed into paper then melted onto paper
