P2 Physics Flashcards
Define current.
The rate of flow of charge.
What does LDR and LED stand for?
LDR = Light dependant resistor
LED = Light emitting diode
What is an electrical conductor?
A material that allows an electrical current to pass through it.
What is static electricity?
When charge builds up on an object and then stays ‘static’ as there is nowhere for the charge to flow away.
What is an electrical insulator?
A material that does not allow an electrical current to pass through it easily.
What are the two things needed in a circuit that are needed to allow current to flow and for the circuit to work?
A power source and a complete circuit.
What is charge?
A property of matter that can be positive or negative, it’s measured in coulombs (c). When charge moves, a current is created.
Where does conventional current flow from?
Positive to negative.
What is resistance?
Resistance is anything that will stop or slow down a current, it’s measured in ohms.
What happens to the voltage and the current in a parallel circuit?
The voltage stays the same across each branch and the current splits down each branch.
Take a few minutes to practice circuit symbols in the book.
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What happens to the voltage and the current in a series circuit?
Voltage is shared between the components and current is the same at any point.
What are some of the applications of thermistors?
Household heating systems, Car engines
What are some of the applications of LDR’s?
Automatic night lights and street lamps, some burglar alarms.
Have a few minutes looking in the book and memorizing the differences between a ceramic resistor, a diode, and a filament lamp.
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Describe what happens to the filament lamp when current is flowing through it?
As current increases, the atoms in the filament lamp begin to vibrate and this increases the temperature. This increases the resistance too which means there is less current for the same increase in potential difference.
Describe what happens to a diode when there is current flowing through it?
A diode only allows current to flow in one direction. No current will flow if it’s pushed the wrong way as the diode’s resistance remains very large. When forward, the diode’s resistance is very large at low potential differences but when potential difference is higher, the resistance quickly drops and the current begins to flow.
Describe what happens to a ceramic resistor when current flows through it?
Potential difference is directly proportional to the current, this relationship is called ohm’s law and is true as the resistance of the resistor is fixed and does not change.
What is meant by an electric power?
Can also be defined as the rate of transfer of energy.
If there is a higher power, what happens to the current?
A higher power means a greater current flows for a given period.
What is meant by a direct current?
When the current only flows in one direction.
Electricity provided by a battery is known as what?
D.C. - Direct current, a typical battery has a voltage of 1.5 V.
What is meant by an alternating current?
When the current is constantly changing direction.
What is the standard UK mains in terms of potential difference and direction of current flow?
Mains electricity is A.C. (alternating current) with a voltage of 230 V and a frequency of 50 Hz
What are the colours of the live wire, earth wire and the neutral wire?
Live wire - Brown, provides 230 V
Earth wire - Green and yellow, Stops appliance casings from becoming live
Neutral wire - Blue Completes the circuit and carries away current
Have a look at the graphs of D.C. and A.C. in the book?
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What is a fuse?
A safety feature on a circuit that contains a wire which will melt if the current gets too high.
Which directions do the three wires go in?
Brown goes right
Blue goes left
Green and yellow goes through the middle, at the top
What happens when a charged object is placed into the field lines of another charged object?
A force is felt - either attraction or repulsion. The size of the force depends upon the strength of the electrical field.
What is a uniform field?
The field between two parallel plates, one positive and the other negative.
What happens when a jumper is rubbed against a balloon in terms of losing or gaining electrons?
The balloon gains electrons and become negatively charged and the jumper loses electrons becomes positively charged. As these objects have opposite charges, there is an attraction force between the jumper and the balloon.
What happens if two insulators (two balloons) have like charges?
A repulsive force is felt - they repel eachother.
What is the polarisation of electrical charge?
Positive ions are a lot more difficult to move on a charged object/wall.
When a charged object, like a balloon, is moved close to a neutral object e.g. a wall, the electrons are repelled and move further into the object.
This leaves an area of net positive charge on the surface, even though the object is electrically neutral overall, this causes an attractive force between the balloon and the wall.
Why are series circuits useful?
They warn you if one of the components has failed. They also use less wiring than parallel circuits.
Why are parallel circuits useful?
If a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel.
