Term
| How have the main sources of domestic energy changed over time? How has this affected society? |
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Definition
Wood- Chem energy to heat&light energy.
-> kept animals at bay, food cold be cooked, humans live in colder climates
Domesticated animals - Mech energy
-> more food, + population, towns developed, animals must be upkept
Wind and water - Mech energy
-> expanded tradin, efficient production of food from grain
Coal - Chem to light&heat
-> steam engine, more alloys, industrial age, pollution, slums,finite
Coal gas - heat coal wout air
-> streets safer at night, batman out of a job
Electric generator - coil rotated in magnetic field
Fuel burning power stations - burning fossil fuels turns turbine of electric generator
-nuclear & hydro electric |
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Term
| How can electrical energy be distributed to remote locations? |
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Definition
| Using the electricity grid |
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Term
| How is electrical energy distributed? |
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Definition
| Transmission lines (and transformers to change the current and voltage to practical levels) |
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Term
| Describe the behaviour of electrostatic charges and the properties of the fields associated with them |
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Definition
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Term
| Describe the behaviour of electrostatic charges and the properties of the fields associated with them |
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Definition
Like charges repel, unlike charges attract. A body becomes charges when it gains or loses electrons.
The direction of an electric field is the direction of the force on a positive charge |
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Term
| What is the SI unit of electric charge? |
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Definition
The coulomb.
It is equal to the charge on 6.25x10^18 electrons |
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Term
| What is an electric field? |
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Definition
The field of force with a field strength equal to the force per unit charge at that point
E= F/q |
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Term
| What is electric current? |
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Definition
| The rate at which charge flows (coloumbs/sec OR amperes) under the influence of an electric field |
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Term
| What is the difference between AC and DC? |
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Definition
AC = alternating current. The charge carriers move backwards and forwards periodically
DC= Direct Current. The net flow of charge carriers moving in one direction |
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Term
| What is electric potential difference / voltage? |
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Definition
The change in potential energy per unit charge moving from one point to the other
(joules/coulomb OR volts) |
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Term
| How does potential difference change at different points around a DC circuit? |
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Definition
| The current loses electric potential energy as it passes through a resistor. The potential difference is not affected by the wires. The potential difference across the power supply is equal to the potential difference across the resistor |
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Term
| What is the difference between an insulator and a conductor? |
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Definition
A conductor contains charge carriers. Charged particles are free to move through the material
An insulator is a material which contains no charge carriers. |
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Term
| How can resistance be determined? |
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Definition
Resistance is the ratio of voltage to current.
R = V/I |
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Term
How do the following factors affect the movement of electricity through a conductor:
-length
-cross-sectional area
-temperature
-material |
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Definition
length- R1/R2 = l1/l2
C-s A- R1/R2 = A2/A1 (inversely prop.)
Temp - Increased temp = increased R
Material - Ag = 0.94 x10^-2
Cu = 1 " "
Al = 1.6 " "
Fe = 5.7 " " |
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Term
| What is the difference between a series and a parallel circuit? |
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Definition
When resistors are connected in series, the same current passes through each resistor
When resistors are connected in parallel, the current divides and passes partly trough each resistor. |
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Term
| What are the uses of ammeters and voltmeters? Why are they connected differently? |
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Definition
An ammeter measures current. It must be connected in series.
A voltmeter measures potential difference across components of a circuit. To do this it must be connected in parallel with the component |
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Term
| Why are there different circuits for lighting, heating and other appliances in a house? |
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Definition
| To avoid overloading electrical wiring, to avoid short circuits, so that if one stops working they don't all stop. |
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Term
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Definition
| The rate at which energy is transformed from one form to another |
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Term
| What is the relationship between power, potential difference and current? |
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Definition
P=VI
Power = Volts X Current |
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Term
| How can you calculate the total amount of energy used? |
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Definition
The amount of energy used depends on the length of time the current is flowing and can be calculated used
W = VIt
Energy used = Volts X Current X time(s) |
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Term
| Why is the kilowatt-hour used to measure electrical energy instead of the joule? |
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Definition
Because the amount of energy used by most devices is too large a number to be realistically used in joule form. KWH = energy transformed by a 1000W device in 1 hr.
W = Pt
=1000 X 3600
=3 600 000 J |
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Term
| How do different magnetic poles interact? |
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Definition
| Like poles repel, unlike poles attract |
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Term
| How do you determine the direction of a magnetic field? |
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Definition
| The direction of a magnetic field is the direction of force on a very small North pole when placed at that point |
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Term
| What is the direction of a magnetic field surrounding opposite charges? |
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Definition
| Magnetic field lines leave the north pole and enter the south pole |
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Term
| What is the right-hand grip rule? |
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Definition
| All electric currents are surrounded by a magnetic field. RHGR determines the direction of the magnetic field based on the direction of the current |
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Term
| How do solenoids and bar magnets produce magnetic fields? |
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Definition
| A solenoid is a wire that has been wound into a closely packed corkscrew shape. The magnetic field of a solenoid is similar to that of a bar magnet, except the current pass through the inside as parallel lines to form closed loops |
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