P5 - Electric Circuits Flashcards
Like charges _____ and unlike charges _______
Like charges repel and unlike charges attract
Static is formed when two _______ rub together
Insulators
The object that loses electrons becomes ________ charged and the object that gains electrons becomes _______ charged
Loses = positively charged Gains = negatively charged
When you rub a polythene rod with a duster, which or the two items becomes negatively charged and why?
Rod = negative because electrons are transferred from the duster to the rod
Describe the electrostatic induction that occurs when a positively charged balloon approaches a wall: (3)
•when a positively charged balloon approaches a wall (neutral), the electrons in the wall are attracted to the surface, creating a negatively charged surface, attracting the balloon
Why do only electrons in an atom create charge and not protons too?
Electrons are free to move and protons are stuck in the nucleus; this is why in a wall during electro static induction, electrons can be attracted or repelled but protons can’t
Why are metals good conductors of electricity?
They have free electrons that can move and carry charge
What aren’t plastics good electrical conductors?
They don’t have as many free electrons as metals so charge cannot be carried effectively
Explain the flow of charge in an electrical circuit (3)
- the cell (battery) provides energy for the electrons
- in a complete circuit, there are free electrons in al the metal components so they carry the charge around the circuit
- electrons carry negative charge so are attracted towards the positive terminal
What types of energy do bulbs produce? (2)
Heat and light energy
What is Electric Current and what units is it measured in?
The rate of flow of charge or the charge flowing per second; measured in amperes or Amps (A)
How many Amps is a Milliamp? (mA)
1 x 10^-3 of an amp or 1/1000 of an amp
What is the equation for charge, including units?
Charge/ Q (coulombs) = Current/ I (Amperes) x time/ t (seconds)
Voltage
The amount of energy needed to make the current flow
Ammeter: What is it? How is it connected?
A device used to measure current which is connected in series either side of a component
Voltmeter: What is it? How is it connected?
A device used to measure voltage which is connected in parallel to the bulb or a component
What is the unit of voltage?
Volts (V)
The larger the voltage, the _____ the current
The larger the voltage, the bigger the current
Power: what is it? What are the units?
Power is the rate at which energy is transferred and is measured in Watts (W)
What is the equation for power?
Power = Voltage x Current
What is potential difference
Another word for voltage; the different in energy per unit charge; a potential difference of 1 volt means that 1 joule of energy is transferred into or out of electrical form per unit of charge
OR
V = J/Q (energy in joules/ charge in coulombs)
Static charge
A form of electric charge which does not move
Resistance
A measure of how much a conductor opposes current
What is the equation for resistance?
Resistance = voltage / current
What is the equation of ohms law?
Voltage = resistance x current
What type of resistors are light bulbs?
Non ohmic resistors
The current is _____ through all components in s series circuit
The same
Adding more bulbs in series does what to the resistance and the current?
It increases resistance and decreases the current
In parallel the current is
Split between the different pathways
Adding resistance in parallel
Reduces the total resistance
With thermistors, the hotter the temperature, the ____ the resistance
Lower
With LDRs, the brighter the light the ____ the resistance
Lower
Magnetic field
The space around a magnet in which a magnetic force acts
How do you increase the current induced by an electromagnet? 3
Increase the speed of motion
Use a stronger magnet
Have more turns in the coil
How can you induce a larger voltage from a generator? 4
Use a stronger magnet
Increase the number of turns of wire
Use an iron core
Increase the rate of the coil being turned
Alternating current
A current where every half term it changes direction
Give an example of an object that uses direct current
Batteries
What is the voltage and the frequent of the U.K. Mains?
230V 50Hz
Why is the uk mains power a.c.? 2
It is easier to generate in large quantities and different fuels can be used in power stations
Give 4 examples of objects which contain motors:
DVD/ CD players, washers and dryers
Explain the motor effect; why does the wire turn in a motor?
When a current flows in a wore near a magnetic field, the wire experiences a force which is at its largest when the current is at right angles to the magnetic field lines
How can you make a motor turn faster? 4
Increase the current
Increase the number of turns in the coil
Get a stronger magnet
Use a soft iron core
Transformer
A component which changes the voltage of any ac power supply
Do transformers work on alternating or direct current and why?
They only work with alternating as a changing magnetic field is needed to induce a voltage in the second coil
How do you work out the efficiency of a power station? Equation
% efficiency = useful power out / power in x 100
Why does the uk national grid transport electricity at high voltages? 2
They are good because high voltage means low current so less wasteful energy transferred and less damage to wires
Why does we use the high voltages of the national grid in our homes?
Everything would melt and we would be killed :)
