Term
| What is the electrical Power equation? |
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Definition
Power = Voltage x Current
P=VI |
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Term
| What is the relationship between pressure and volume in a closed system? |
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Definition
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Term
| What is the relationship between power, energy and time? |
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Definition
| Energy(joules)=Power(watts)xtime(seconds) |
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Term
| What is the energy transferred by an electric fire connected to a 230V mains which carries 5A and which is on for 20min? |
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Definition
Power = Volts x Amps
= 230 x 5 =1150W
Energy = power x time(in seconds)
= 1150 x 1200
=1380000J = 1.38MJ |
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Term
| How can an insulator be charged by friction? |
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Definition
| By rubbing it with a cloth. |
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Term
| What are the units of frequency? |
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Definition
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Term
| What is the unit of speed? |
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Definition
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Term
| What is the unit of wavelength? |
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Definition
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Term
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Definition
| wave speed(m/s) = frequency(Hz)x wavelength(m) |
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Term
| What is the relationship between voltage and number of turns on a transformer? |
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Definition
| V primary/Vsecondary=Turns pimary/turns secondary |
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Term
| How are step up transformers used in the electrical grid? |
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Definition
| Voltage is stepped up at the power generating station before distribution. |
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Term
| When are step down transformers used in the electricity grid? |
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Definition
| Before the voltage is supplied to consumers it is reduced to 230V from high voltages eg 400kV |
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Term
| What material is used for the core of a transformer? |
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Definition
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Term
| work out the frequency of a wave of length 2m travelling at 330m/s |
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Definition
frequency=wavespeed/wavelength
=330/2
=165Hz |
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Term
| Which type of signals carry more information, analogue or digital? |
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Definition
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Term
| Why is electricity transmitted at high voltages? |
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Definition
| this reduces the current required so reduces the energy lost due to heating effects |
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Term
| Why is electricity used in the home at low voltages? |
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Definition
| safer - less likely to cause death by electrocution |
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Term
| What is the voltage at the secondary of a transformer attached to a 230V supply if the primary coil has 500 turns and the secondary has 25 turns? |
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Definition
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Term
| Which of these are transmitted by waves? Matter, energy,information |
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Definition
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Term
A transformer is used to light a 3V bulb from a 24V supply. Is it a step up or step down transformer?
Calculate the number of turns on the secondary if there are 400 turns on the primary. |
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Definition
step down
T2 = T1xV2/V1
= 400x3/24
= 50turns |
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Term
| A container of volume 1 litre contains a fixed mass of gas at 500N/m2. If the volume is reduced to 250cm3 what will be the new pressure of the gas? |
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Definition
P2=P1xV1/V2
=500x1/0.25
=2000N/m2 |
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Term
| What happens when waves pass through a narrow gap or past an edge? |
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Definition
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Term
Which type of waves show diffraction effects?
1. Sound
2. Light
3. Both sound and light |
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Definition
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Term
| What does Boyle's law state? |
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Definition
| The pressure of a fixed mass of gas is proportional to the volume of the gas. |
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Term
| How do the particles in a gas move? |
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Definition
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Term
| How does a gas exert pressure? |
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Definition
| By random collisions of the gas particles with the walls of the container or other surfaces. |
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Term
| describe the relationship between the applied force and extension of an elastic object |
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Definition
| Extension is directly proportional to applied force (Hooke's law) |
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Term
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Definition
| the energy transferred per unit charge passed ie a volt is a joule/coulomb |
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Term
| What happens to a current carrying wire in a magnetic field? |
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Definition
| A force is exerted upon it perpendicular to both the direction of the field and the direction of current flow |
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Term
| Describe how electrostatic charges interact. |
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Definition
| Like charges repel; unlike charges attract |
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Term
| What happens when an insulating material such as amber is rubbed with a cloth? |
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Definition
| It becomes charges due to the transfer of electrons. |
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Term
| Whcihc types of material are insultaors and which are conductors? |
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Definition
metals are conductors
plastics, glass, wood and other non-metals are mainly insulators |
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Term
Describe a situation in which build up of electrostatic charge may be dangerous.
How is the danger reduced or eliminated? |
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Definition
Refuelling an aircraft: friction of the fuel in the pipe leads to build up of charge between the aircraft and the ground. A discharge could cause fire/explosion.
Earthing the aircraft by connecting it to the ground with a wire
(Car body - after driving: again earth)
(synthetic fabrics rubbing on car seat charge passenger)
(lightning - use lightning conductor to leak charge to air) |
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Term
| What is an electric current? |
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Definition
| Current is the rate of flow of charge.It involves the flow of electrons in metals or ions in electrolytes. |
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Term
| What is the charge on an electron? |
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Definition
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Term
| Some common salt is dissolved in water. A potential difference is applied to two electrodes placed in the salt solution. Explain what will happen. |
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Definition
| A current will flow as positively charged sodium ions are attracted to the cathode(negative electrode) where they collect electrons. At the same time negatively charged chloride ions are attracted to the anode(+ve electrode) where they release electrons. |
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Term
| How can the insulator solid lead bromide be made to conduct a current? |
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Definition
| Melt it so the lead and bromide ions can move to the electrodes. |
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Term
| What is total internal reflection and when does it occur? |
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Definition
| When a ray of light strikes a surface between two media at an angle such that all of the light is reflected back into the medium in which the light is travelling. This is called the critical angle |
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Term
| Describe how total internal reflection is used. |
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Definition
1) cats eyes - light from headlight reflected back to car by prism shaped glass in cats eye
2) in optical fibres - light ray strikes side of fibre and all is reflected along the fibre so no loss of energy occurs - eg in telephone cables, endoscopy etc |
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