Electricity Flashcards
What happens when two insulating materials are rubbed together
A charge is induced
What does a flow of electrons cause
A current
What happens if electrons ‘jump’ between an object and a metal
Sparks are created
How does an aircraft get a charge
Either from air molecules rubbing during flight or through the fuel flowing through the fuel pipe
How does charge help to evenly distribute things like paint, ink in printers, pesticides etc
- The like charges repel so the droplets push away from each other, ensuring there are no clumps of the substances
- The droplets are electrostatically attracted to the surface they are being dispensed on, so the adhesion and coverage is better, especially on uneven surfaces
What is the equation linking power, current and voltage
Power (W) = current (A) x voltage (V)
P=IV
What is the equation linking current, charge and time
Current (amperes(A))= charge(coulombs(C)) x time (seconds)
What is the definition of current
The rate of flow of charge
What is the definition of voltage
The energy produced per unit time
What is a fuse
A small thin piece of wire that will melt if too much current passes through e.g. if more than 3 amps is passed through a 3 amp fuse, it will melt, so the circuit is broken. It is a safety measure
What is the live wire
The brown one - carries the electricity. You will shit yourself if you touch it
What is the neutral wire
It is the blue one, which completes the circuit
What is the earth wire
It is green and yellow - it provides the path of least resistance to the ground
How does the temperature of water affect the resistance of a thermistor
As the temperature goes down, the resistance increases
What is a thermistor used for in real life and why
Fire alarms - high temperature = low resistance, which allows the current to flow through the circuit, so the alarm rings
What is the circuit symbol for a thermistor
A rectangle with a diagonal L shape (see google for better representation)
What are the I-V characteristics of a wire
Directly proportional = straight line
What are the I-V characteristics of a wire
Directly proportional = straight line y=x
What is the I-V graph of a diode
Stays on the x axis until the origin, then goes exponential (see Series and Parallel Circuits note for better representation)
What is the I-V graph of a light bulb
(see Series and Parallel Circuits note for better representation)
What is the I-V graph for a fixed resistor
(see Series and Parallel Circuits note for better representation)
What is the I-V graph for a fixed resistor
(see Series and Parallel Circuits note for better representation)
What is the I-V graph for a fixed resistor
(see Series and Parallel Circuits note for better representation)
What are ohmic conductors
Components that have an I-V graph that follow Ohm’s Law (V is proportionate to V) (wires and fixed resistors)
Describe an experiment to investigate the I-V characteristics of a fixed resistor/wire/light bulb/diode. Use a diagram to aid explaination.
- Set up a circuit containing a variable resistor, a battery, an ammeter and the set component (e.g. a light bulb).
- Record the current and voltage
- Adjust the variable resistor to change the. Ur Trent and voltage through the lamp. Record the new values
- Repeat step 3 until you have several pairs of values
- Swap the connections on the battery. The current and voltage through the lamp should now be negative
- Repeat step 3
- Repeat step 6 until you have many pairs of values
- Repeat the experiment for reliability
- Start again but with another set component (e.g. a wire)
- Draw the diagram on note: Series and Parallel Circuits
What is an LDR
A light dependent resistor
What is intensity
A measure of the power per unit area. It is measured in Watts/square meter
How does an LDR work
As light intensity increases, resistance decreases
What is the current in a series circuit when the same component are used
The same all over, because the charges per second in every section is the same
What is ohms law
V=IR
Voltage = current x resistance
What is the unit for current
Amps
What is the unit for resistance
Ohms (Ω)
What is the unit for voltage
Volts (V)
What is the voltage across the junctions in a parallel circuit and why
The same - this is due to the conservation of energy.
How do you work out total resistance
1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc etc
What equation links power energy and time
Power = energy/time
What equation links power, current and voltage
Power = current x voltage
P = IV
What equation links energy transferred, current, voltage and time
E = IVt
What equation links power, charge, voltage and time
P=QVt
What is the equation E = QV(t^2)
Energy transferred = charge x voltage (per second)
What equation links charge current and time
Charge = current x time
Q = IT
What is EWAUSS
- Equation
- Workings
- Answer
- Units
- Scale
- Sense Check
Describe current in solid metallic conductors
A flow of negatively charged electrons
How are positive and negative electrostatic charges produced
By loss (positive) or gain (negative) of electrons
How are insulating materials charged
Friction
What are the forces between unlike charges
Attraction
What are the forces between like charges
Repulsion
Name some electrical conductors (3)
- Copper
- Iron
- Aluminium
Name some electrical insulators (2)
- Plastic
- Rubber
- Air
Which metals do not conduct electricity
None
Name 1 substance that is an electrical conductor but is not metal
Graphite
What is electrostatic phenomena
Electrostatic phenomena arise from the movement of electrons, which can gain or lose electrons, leading to the creation of electric charges. This interaction of charges causes attraction and repulsion, and various methods exist to charge objects through friction, conduction, and induction.
What is induction of a charge
The redistribution of charge without contact e.g. bringing a negatively charged rod close to a metal ball will cause the electrons in the sphere to move away, so the side of the sphere closest to the rod will become positively charged.
Can protons move between materials
No
How can electrostatics be dangerous
Build up of charge can create sparks, which can cause fire
Why is electrostatic charge dangerous when fuelling aircraft and tankers
As the fuel moves through the fuel pipe, friction is generated, so a charge is generated, which could result in a spark and the fuel catching on fire.
How is the potential for static electricity to build up in the fuel pipe mitigated (6)
- Grounding the aircraft and fuel truck with bonding cables
- Ensuring continuous contact between the aircraft and fuel truck
- Grounding the fuel pipe
- Using more conductive fuel
- Fuelling the aircraft slowly
- Preventing turbulence when fuelling
What are amperes (A) the units for
Current
What are coulombs (C) the unit for
Charge
What is insulation on household wires
A protective plastic coating that surrounds electric wires to stop people getting electrocuted and to prevent fires
What is double insulation for electricity
2 layers of insulation (plastic or rubber) protect users from electric shock. There is no need for grounding if double insulation is used
Which insulation requires grounding: insulation or double insulation?
Insulation
What is earthing
A safety system where exposed metal parts are connected to the ground, to prevent electric shock
What are fuses
A thin piece of wire, a safety device has been melts if too much current is passed through it. E.g. if more than 3A is passed through a 3A fuse, it will melt, breaking the circuit
What are circuit breakers
An electrical safety device that automatically shuts off the flow of electricity in a circuit when it detects an overload or a short circuit. Unlike fuses, they can be reset, so are not single use
Which is single use: fuses or circuit breakers
Fuses
How is electric heating used in a domestic context
- Space heaters (portable heaters
- Radiators
- Underfloor heating
- Boilers
What does current flowing through a resistor result in
The electrical transfer of energy and an increase in temperature (used to heat the home)
Is mains electricity DC or AC
AC
What type of current do cells and batteries provide
DC
What is AC
Alternating current - the direction of the current is reversed multiple times per second
What is DC
Direct current - the direction of the current is constant
What components can be used to show the presence of current in a circuit and why
Lamps and LEDs - if they light up there is current present
