Electricity and circuits Flashcards
(40 cards)
What is current?
The rate of flow of charge of electrons.
-It will only flow through electrical components if there is a potential difference and the circuit is complete
What is potential difference?
The driving force that pushes charge. It is the energy transferred to a component per columb charge that passes through it
What is resistance?
How easy it is for current to flow through objects. It opposes current as current does work against resistance. This causes an electrical transfer of energy
What is the equation that links charge,current and time?
Charge (Q) - (C) = current (I) - (A) x time(T) - (S)
What is the equation that links current, potential difference and resistance?
Potential difference (V) = current (I) x resistance(R)
What affect does current have on a resistor?
As current flows through a resistor, it heats up due to collisions between electrons and ions in the lattice that makes it up. This is because the ions vibrate more making it harder for electrons to get through the resistor as there are more collisions (if too hot no current is able to flow)
-resistance increases with temperature
What is a ammeter?
Measures current (in amps) flowing through the component -can be put anywhere is a circuit
What is a voltmeter?
Measures potential difference across the component -it must be places in parallel with the component under test
What is Ohm’s law?
Current is directly proportional to the voltage when the temperature stays constant
What happens when investigation a filament lamp?
The current isn’t directly proportional to the voltage. This means it doesn’t follow Ohm’s law and the graphs isn’t straight.
-resistance is higher as greater voltages as temperature increases as the lamp heats up
What happens when investigating diodes?
- current only flows in one direction and only when the voltage is about 0.6V
- distance is much greater in one direction than the other
- the graph is non-linear curved
- doesn’t follow ohm’s law
What happens when investigating a thermistor and LDRs (resistors)?
Thermistors (temperature dependent resistor) have a low resistance at high temperatures
-used for temperature detectors e.g. car engines
LDRs (light dependent resistor) resistance decreases as light intensity increases
-used for automatic night lights
(BOTH FORM ASYMPTOTE GRAPHS)
What us a series circuit?
All components are connected in a line, end to end, between the +Ve and -Ve of the power supply (except voltmeters)
- if you remove any component the circuit breaks and stops working
- only one branch
What are the rules and patterns of series circuits?
- more supply of V when there are more cells in the circuit
- current is the same everywhere and is dependent of V and R
- voltage of power supply is shared between components
- resistance increases as resistors are added as they have to share V, this decreases current
What is a parallel circuit?
Each component is individually connected (except ammeters which are always in series). Therefore, if one is removed it will have hardly any affect on others.
What are the rules for parallel circuits?
- potential difference is the same across all components
- current is shared between branches
- junctions are where the current splits and rejoins (total current into a junction is equal to total current leaving)
- total resistance decreases if you add a second resistor as current has more than one way to flow (V=IR)
Where is energy supplied from in circuits?
Energy is supplied to the charge at the power source and the charge gives up this energy when it falls through any potential drop in components
-component offers a resistance so charges loose energy when they
go through it leading to a potential difference.
-larger the current or PD the more energy transferred to it
What is the equation for energy transferred?
Energy transferred = current x voltage x time
Or
Energy transferred = voltage x charge
What is power?
The rate of work done (how many joules of energy are transferred per second).
Total energy transferred depends on how long the appliance is on for and it’s power
What is the equation for power and electrical power? And if you don’t have potential difference?
Power (W) = energy transferred(J) / time (s)
Electrical power (W) = current (A) x voltage (V)
- Electrical power (W) = current squared (A) x resistance (ohm’s)
What is power rating?
Tells you the maximum amount of energy transferred between stores per second when in use
-the lower the power rating the less electricity used so it is cheaper to run
What is A.C.?
Alternating current, where the movement of charges if constantly changing direction and are produced by alternating voltages (going between positive and negative)
-provided by mains power supply (230V) and frequency of 50Hz-electrical energy input
What is D.C.?
Direct current where the movement of the charges is only in one direction created by direct voltage (either all positive or all negative)
-it is provided by batteries and cells -chemical energy input
What is the neutral wire?
The blue wire which complete the circuit and where electricity usually flows out from
- always goes to the left at 0V
- goes to power station
