# Physics- Circuits

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• Created by: FireDwarf
• Created on: 18-09-13 17:53
What is a charge carrier?
a charged partical that moves through a substance when a PD is applied across it
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What is current?
The rate of flow of charge ( when one coulomb passes a certiain point in a circuit in one second)
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What direction does normal current flow? Conventional?
- to + and + to -
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What is one coulomb in terms of charge?
Charge of 6.2 x 10^18 electrons
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What is the charge of 1 electron?
-1.6 x 10^-19
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What is Potential diffrence?
Potential diffrence is the energy transferred per unit of charge.
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Another descripton?
It is the difference of electrical energy between two points ( when the charge carrier comes from the negative and comes into the positive)
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How to work out charge?
Charge is the number of electrons x the charge of one electron (-1.6 x 10^-19)
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What is Ohms Law?
The voltage directly across a metalic conductor is proportional to the current through it, providing the physical conditions do not change
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Example of a physical condition?
Temperture
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What is an ohmic conductor?
Something with a fixed resistor or a wire
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Ohmic conductor graph?
Voltage is proportional to current
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Current voltage graph (non-ohmic) Filament bulb
Wavey line
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why?
Current and PD are not directly proportional. As current increases, the electrons move faster, which causes more energy to be passed to the ions in the wire, causing them to move more (higher temp), more residence therefore less current flowing
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Non-ohmic diode- what?
Diode limits the current to only going in one direction due to a high resistance in the reverse direction
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Whats the leakage current?
The leakage current is when there is enough potential diffrence for a current to flow
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Thermistor
If temperature is increased, resistance decreases
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Light Dependent Resistor
Increase the luminosity decrease resistance
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What is a superconducting material?
A material that has zero resistivity at and below crtical temperture. The crtical temperture is dependant upon the material.
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Whats the PD?
When the current flows, it has no PD across it because its resistance is zero. Current has no heating effect.
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Highest critical temperture?
150k
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What are the high temperture superconductors above?
77k
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What are they used for?
Strong super conducting magnetts with a strong magnetic field & power cables that transfer large currents & cables losing no energy
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How?
can sustain large current because there is no resistance which would reduce current. Allows therefore for strong field and efficient. No energy lose, no resistance.
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Two Rules about the not losing current/PD in a circuit.
at any juction in a circuit, the total current leaving the junction is equal to the total current entering the junction.
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ddd
2 or more componants in a circuit in series, total PD is sum to the total of the two componants
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In a series circuit, what is shared and what is equal?
Current is shared (I0=I1=I2), PD is split V0= V1+V2
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In a parrell
Current is split (I0= I1+ I2), Voltage is the same in each series in parrell (V0=V1=V2)
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Resistance in series?
R0= R1+R2
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Reistance in Parrell?
1/R= 1/R1 + 1/R2
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What is Emf?
A giver. It is the electrical energy per unit of charge provided by the source.
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What is P.D?
Electrical energy per unit of charge delivered by the source to the componant.
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What is lower, Emf or Pd? Why?
P.D is less then EMF when a current passes through the source. Diffrence is due to internal resistance , r, of the source.
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What is internal resistance due to?
Chemicals inside the cell offer a resistance to the flow of current.
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Formula for EMF?
e = I(R+r)
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What is Lost P.D?
The energy lost between the EMF and the PD ( V= Ir)
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What is P.D across cell terminals?
The energy per unit of charge delivered to the componants (V= IR) (e= v+v)
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What is power delivered to the resistor?
P= IV, P= V2/R, P=I^2R
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Power wasted by the cell?
Power which is lost from the EMF to the PD. p= Iv p= v^2/r p=I^2r
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max current?
The current if there was no external resistance = I= E/r
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EMF is series? r in series?
Total EMF= Sum of EMF , r = Sum of internal resistance
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EMF in parrell? r in parrell?
EMF is the EMF of one cell, r = r/n (n = number of loops NOT CELLS)
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How do we find out the PD of each resistor?
Its equal to the ratio of of the two resistors (compared to the total PD).
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What is a PD divider?
2 or more resistors in series with each other, with a source of fixed PD. The PD is then divided between the componants of the circuit.
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How can it be used with suitable componants?
To supply a PD which is fixed, supply a varied PD, supply a pd which changes in physical conditions.
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What does the potential divider do?
Prevents the fluctuation of current, as with a variable resistor in series, the current fluctuates.
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How can a potential divider be used?
as a temp sensor or a light sensor. With a fixed temp of thermistor constant, the PD is divided between the thermistor and variable resistor. By adjusting the variable resistor, the thermistor can be set at any value.
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## Other cards in this set

### Card 2

What is current?

#### Back

The rate of flow of charge ( when one coulomb passes a certiain point in a circuit in one second)

### Card 3

#### Front

What direction does normal current flow? Conventional?

### Card 4

#### Front

What is one coulomb in terms of charge?

### Card 5

#### Front

What is the charge of 1 electron?