Circuits/ Electricity Flashcards
What is potential energy
Stored energy
What is voltage
- The potential energy difference between two locations in the units volts (V)
What is potential difference
The amount of energy each unit of charge carries. Potential difference causes current to flow
What is current
The rate of charges move through a conductor
Q = It -> I = Q/t -> the rate of energy flow
What are the seven base units
Metres (m)
Kilograms (kg)
Seconds (s)
Ampere (A)
Kelvin (K)
Moles (mol)
Candela (Cd)
What are the base units for a newton
kgms^-2
What are Joules in base units
kgm^2s^-2
Why do electrons flow but protons and neutrons don’t
Electrons are on the outside of the atom so I’m more easily transferred
What is resistance
How difficult it is for electrons to flow in ohms
What has more resistance for water to flow a hose or a giant pipe
The hose. this is because the giant pipe has a larger cross-sectional area whereas the hose has a small cross-section area therefore the water is hitting more air particles in the hose
Conductors or insulators have high resistance
– Conductors have low resistance
– insulators have high resistance
Name three formulas for power
P = I^2R
P = VI
P = V^2/R
which way does conventional current flow
From positive to negative
Which way does actual current flow
From negative to positive
What useful feature does a voltmeter have so that it can measure voltage efficiently
Want me to has a higher resistance so that current cannot go through it therefore a better voltage reading can be measured
One path of a circuit has three ohms of resistance another part of a circuit has six ohms of resistance which way or the electrons most likely flow
The electrons will follow the path of the lowest resistance therefore this is the path with three ohms
What is the formula for resistance in series
R1 +R2 = RT
What is the formula for resistance in parallel
1/R1 + 1/R2 = 1/RT
where RT is smaller than the smallest resistance
What are the three factors affecting resistance in a wire
Length
Material
Cross-sectional area
What is the formula involving resistance and resistivity
R = pL/A
where,
R = resistance
p = resistivity of material
L = length of wire
A = cross-sectional area
What does resistivity mean
How many electrons there are
What is it called when a component has a linear relationship between current and voltage
Ohmic
What does the current-voltage graph look like for a resistor
A diagonal straight line going through the origin of the graph. This graph is ohmic
What does the current-voltage graph look like for a filament lamp
An S-shaped curve going through the origin from the third quadrant to the first
What does the current-voltage graph look like for a thermistor
A curve starting almost vertical in the top right hand corner of the first quadrant before curving down till it looks almost diagonal going through the origin before curving back and looking vertical again but in the bottom left-hand corner of the third quadrant
What does the current-voltage graph look like for a diode
An exponential graph that curves upwards only from the origin into the first quadrant
Explain why the graph for a filament lamp looks that way
The filament is typically made of tungsten, a metal.
As the filament heats up due to the current flowing through it, the metal atoms in the filament vibrate more intensely because of the increased thermal energy.
These vibrating atoms interfere with the movement of the electrons, making it harder for them to flow through the filament.
As a result, the resistance increases because the electrons face more obstacles while moving through the hotter, vibrating filament.
Explain why the graph for a diode that way
A diode only allows to flow in One Direction therefore the graph is only seen in the first quadrant
Explain why the graph for a thermistor looks this way
At higher temperatures, more energy is available in the material, which excites the electrons.
These excited electrons become free to move, meaning there are more charge carriers available to conduct electricity.
With more free-moving electrons, the material becomes better at conducting electricity, so the resistance goes down.
What is a useful feature for an ammeter to have in order to measure current
It needs to have a low resistance therefore more current will pass through the ammeter
On an ohmic I-V graph, two lines are drawn going through the origin. One line is steeper than the other, which line has the lowest resistance
Line one will have a lower resistance because for the same amount of voltage it is allowing more current to pass through the wire, whereas the second line is allowing a lot less to flow through the wire for the same amount of voltage
what is an ohmic conductor
A while or component in which the resistance is constant. The temperature must be constant
What does it mean if there are more length of coil in a resistor
There are on a resistor the higher the resistance
What is the relationship between light and resistance for a light dependent resistor
As the amount of light increases the resistance decreases
Why does the resistance decrease when the amount of light increases in a light dependent resistor
As the amount of light increases (heat energy), it breaks the electrostatic attraction between the nucleus and the electron. The electrons become free to be localised and move, carrying a charge. Therefore at larger amounts of light there is lower resistance because there is higher current
What is the valence band
In solid materials, particularly in semiconductors and insulators, electrons occupy different energy levels.
The valence band is the highest range of energy levels where electrons are still tightly bound to atoms and cannot move freely through the material.
Electrons in the valence band do not conduct electricity because they are not free to move.
What is the conduction band
The band where the electrons can move freely and carry a charge
What is the distribution of electrons between the conduction and the valence band in a conductor, semiconductor and an insulator
In a conductor:
There are more electrons found in the conduction band than in the valance band. This is because a conductor can easily carry a charge therefore have more delocalised electrons
Semiconductor:
The number of electrons in the conduction and valence band are equal
Insulator:
The number of electrons in the valence band is more than in the conduction band. This is because an insulator is less prone to conducting electricity
Using knowledge of the valence and conduction band explain why as light energy increases, there is more current in a light dependent resistor
As the light energy increases of a light dependent resistor, more energy supplied and the electrons move up into the conduction band from the valence band
Explain what a conductor is in terms of energy gaps
A conductor has non-existent energy gaps, allowing electrons to flow easily, which is why they conduct electricity so well.
Explain what an insulator is in terms of energy gaps
An insulator has large energy cap between bands, this means the electrons need more energy to flow into the conduction band, which is why they do not conduct electricity so well
Explain what is meant by semiconductor in terms of energy gaps
There is a medium energy gap between the bands
What is a variable resistor
A variable resistor is able to change the resistance of a wire with a slider
What is a potentiometer
A component that divides the potential difference
How does a potentiometer work
A potentiometer has three terminals. Terminal one is connected to terminal three for the flow of electrons. Terminal two is connected in a loop to itself. There is an error placed on loop too. You can move the arrow to increase the length that the have to flow through. By increasing the length you are increasing the resistance because the electrons to flow further. In the loop between terminal one and three there is a resistive material in order to measure the resistance
How does potential difference affect current in a potential divider
At larger potential differences more energy is required for current to flow through
What is a potential divider
A component that allows circuits to tune the voltage that has been delivered to the desired component
In the resistance of the first resistor is 30 ohms, the resistance of the second resistor is 10 ohms. How would you say the voltage is split? The resistance in the first resistance increases how would this affect the voltage and why?
3:1
If the resistance in the first resistor increases the voltage will increase in order to push the current along, as the current is the same along a series circuit
