# P2.3 and P2.4

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What happens when electrically insulating materials are rubbed together?
Electrons are rubbed off one material on deposited on the other. As electron have a negative charge the material that has gained electrons becomes negatively charged + the one that has lost electrons becomes positively charged.
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What effect does distance have on the attraction between charged materials?
The closer the materials are the stronger the attraction
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What are ammeters and voltmeters?
Ammeters are placed in series with the component to measure the current through the component in amps/ amperes/A . Voltmeters are always placed in parallel to a component to measure the pd across a component in volts
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What is resistance?
Opposition to the current flow in ohms Resistance = PD / current
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Which equation relates PD and work done and charge?
Pd = work done (J) / charge (C)
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What is ohms law?
When the current is directly proportional to the voltage across a resistor. The component obey ohms law. It is ohmic conductor because the resistance is constant.
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Describe the current-potential graph for a filament light bulb.
It is not directly proportional. The resistance of the filament increases as the current increases because the temperature also increases. Reversing the Pd makes no difference to the curve
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Describe the current-potential graph for a diode
It is not directly proportional. It only flows in one direction because there is a large resistance in the other direction so the current is zero.
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What is the equation for current?
Current(A) =Charge(C) /time(s)
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Describe the resistance of the LDR
As the light falling on an LDR gets brighter, the resistance decreases
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Describe the resistance of a thermistor?
As the temperature increases, the resistance of a thermistor decreases.
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What is a series circuit?
Components are connected one after another, so if there’s a break anywhere in the circuit the charge stops flowing.
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What are the key points for the components in a series circuit?
Current is the same in each component. Adding the Pd’s = total Pd of supply. Adding the resistances = total resistance of circuit. Bigger the resistance of a component, the bigger its share of the supply Pd.
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What is a parallel circuit?
Each component is connected across the circuit-if break in 1 part of circuit, charge can still flow in other parts.
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What are the key points for components in parallel circuits?
Total current = sum of currents through components. Bigger the resistance, smaller the current. Pd same across each component.
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What happens to electrical energy when charge flows through an appliance ?
Electrical energy is transferred into other forms of energy. In a resistor the electrical energy is transferred to the resistor so the resistor becomes heat.
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Why are electrical dangerous?
Because they can cause electric shocks and fires.
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How do you measure voltage?
Measure the amp of a wave and multiply by the y-sensitivity
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How to measure time period
Measure the wavelength and multiply by the time base period and convert into seconds.
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What is direct current and alternating current?
What is direct current and alternating current?
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Name two equations involving power?
P= V x I P= I2 X R
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Name an equation involving energy?
E = V x I x t E=V X Q
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Describe all of the prefixes?
Look at the prefixes sheet
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What are the key components of mains circuits?
Frequency in UK = 50 Hz 9 changes direction 50 times a second. The live wire alternates between +325V and -325V in direct current  Voltage = 230V.
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What is the equation for the frequency?
Frequency = Hz = 1/t
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Why is a 3 pin plug made out of plastic and the pin s made of brass?
Plastic is a good insulator + Brass is a good conductor, is hard + resistant to corrosion.
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Label the plug
Look in the book
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What is the difference between a two core plug and a 3 core plug?
A 3 core plug has earth, neutral and live wires whilst a two core plug doesn’t have an earth wire because they have double insulation, they have plastic wiring rather than metal casing.
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Why do appliances need to be earthed?
Because it a fault develops and the live wire touches the case, the case becomes live and could give a shock to anyone that touches it.
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Why a fuse is always fitted in a series with the live wire?
Because if a fault develops in an earthed appliance, a large current flows to earth and melts the fuse disconnecting the supply.
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Why does the rating of the fuse have to be slightly high than the current
Because if it is not then the fuse will melt as soon as the appliance is switched on, but if it is too much higher than the fuse will not melt when the current gets high
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What is a circuit breaker?
This can be used in place of a fuse and it is an electromagnetic switch that opens and cuts of the supply if the current is bigger than a certain value
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What is an RCCB
This is similar to fuses but better as they are more sensitive and faster, they sense any difference in current between the live wire and neutral wire and disconnects the circuit if there is.
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What is power?
Power is the rate at which energy is transferred into other forms of energy Power(W) = Energy Transferred(J)/Time(s)
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why are appliances earthed?
The earth wire creates a safe route for the current to flow through if the live wire touches the casing.
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what does the current though a component depend on?
The current through a component depends on its resistance. The greater the resistance the smaller the current for a given potential difference across the component
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why are the wires in a cable made of copper?
Because it is a good conductor of electricity and it is ductile
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## Other cards in this set

### Card 2

#### Front

What effect does distance have on the attraction between charged materials?

#### Back

The closer the materials are the stronger the attraction

### Card 3

#### Front

What are ammeters and voltmeters?

### Card 4

#### Front

What is resistance?

### Card 5

#### Front

Which equation relates PD and work done and charge?