Particles at work part two Flashcards
Electrical components
the equation for resistance of an appliance
Resistance R (ohms) = potential difference V (volts) / Current I (Amps)
How can the curve potential graph of a filament lamp show its not an ohmic conductor?
Because the line curves away from the Y axis/ it is not directly proportionate.
Does reversing the current through a filament lamp affect the curve of the curve-potential graph?
No it does not, because the resistance is the same for the same current, regardless of the direction of its flow.
What happens when a filament lightbulb fails?
It happens when the lamp is switched on, resistance goes from low to high as current begins to flow, if the current is too big then it burns the filament out.
Explain the curve of current-potential for a diode
The re is a flat line, then a sudden sharp increase in current with small amount of increase in potential difference. The line curves towards the Y axis, it is not proportionally directional. The resistance changes as the current does, but in reverse direction, current is zero. So current in reverse direction is a lot higher than its resistance in the forward direction.
What is a thermistor
a temperature dependent resistor, its resistance decreases if its temperature increases and vice versa.
What happens to the resistance of an LDR if the light intensity increases?
Its resistance decreases.
Factors for considering result of a test about temperature and solar radiation to be only applicable to the test’s location
Some energy is used to heat the metal pan and energy is also transferred to the surroundings, and solar radiation may not remain consistent during the investigation (eg angle of light and intensity)
Which equation uses a square root to obtain it’s rearranged values?
to obtain V from V squared in kinetic energy = 0.5 x Mass x Speed (vsquared)
What are the current and potential difference circuit rules?
In a series circuit, the same current passes through each component. In a series circuit, the total potential difference of the power supply is shared between the components.
What is the rule for series circuits if there is more than one battery?
Total potential difference of cells in series is the sum of the potential difference of each cell.
What is the resistance rule for components in series?
The total resistance of two or more components in series is equal to the sum of the resistance of each component.
(R total = R1 +R2 etc)
What happens to resistance when you add more resistors?
Adding more resistors in series increases the total resistance because the current through the resistors is reduced and the total potential difference across them is unchanged.
What is the rule for current for a parallel circuit?
The total current through the whole circuit is the sum of the currents through the separate branches.
What is the rule for potential difference for a parallel circuit?
For components in parallel, the potential difference across each component is the same.
What is the rule for resistors in parallel?
The total resistance of 2 + components in parallel is less than the resistance of the resistor with the least resistance.
What happens to resistance if you add more resistors in a parallel?
it decreases the total resistance because the total current through the resistors is increased and the total potential difference across them is unchanged.
What do you call current in a circuit that flows only in one direction?
Direct current
What is an alternating current?
An alternating current repeatedly reverses its direction. Its frequency is the number of cycles it passes through each second.
Which kind of circuit has both a live wire and a neutral wire?
A mains circuit.
Why does the current through a mains appliance alternate?
Because the mains supply provides an alternating potential difference between the two wires. In comparison, the pd in direct current circuits do not change direction.
Where is the earth wire earthed in a mains circuit?
At the local electricity substation.
What is the pd of the live wire and earth wire called?
The potential or voltage of the live wire.
Why is the live wire dangerous?
Because its potential repeatedly changes from + to - and back every cycle.
How to measure the frequency of an ac supply?
1/time taken for 1 cycle
What is the outer casing of a plug/socket/mains circuits made of?
hard wearing electrical insulators- it needs to be because the plug contains live wires.
What is the composition of a plug?
Plastic coating with the live pin, the neutral pin and the earth pin stick out through the plug case. The pins are made of brass because the brass is a good conductor that doesn’t rust or oxidise. The pins should not touch. The plug contains a fuse also between the live pin and live wire if it melts it cuts the live wire off.
When does the earth wire carry a current?
Only when there is a fault in the circuit.
Which pins do the brown, blue and green/yellow wire connect to?
Brown connects to live pin, blue connects to neutral pin and green/yellow connects to the earth pin.
What does the earth wire do?
it connects to the longest pin and is used to earth the metal case of a mains appliance.
What is a short circuit?
If the live wire touches the neutral wire, a large current passes between them as a new short circuit that causes the fuse to blow and cuts the current off.
What are the calculations for power?
Power = energy transferred (J) / time (s)
or power supplied = current x potential difference
power = current squared x resistance
How do you calculate the correct rating for a fuse?
electrical power (watts) / potential difference (volts) = fuse rating
