P2.3 + 4 or 4 and 5

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What happens when two electrically insulating materials are rubbed together?
Electrons are rubbed off one material and deposited on the other. As electrons have a negative charge, the material that had gained electrons becomes negatively charged + the one that has lost electrons becomes positively charged.
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Compare what happens to two objects that have opposite or the same charges are brought together.
Opposites attract and objects with the same charge repel each other. The bigger the distance between the objects the weaker the force between them
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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 with the component to measure the potential difference in volts/V.
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What is resistance?
Opposition to the current flow in Ohms (Ὼ). Resistance = Pd(V) ÷ Current(A)
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Which equation relates potential difference, work done and charge?
Potential difference (V) = Work done (energy transferred) (J) ÷ Charge (in coulombs(C)
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What is Ohms Law?
When the current is directly proportional to the potential difference (pd) across the resistor. Any component that obeys Ohm’s Law is an Ohmic conductor.
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Describe the current-potential graph for a filament bulb?
It is a curve as the current is not directly proportional to the pd. 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?
The current through a diode flows in one direction. In the reverse direction the diode has a very high resistance so the current is zero.
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Describe the resistance of a light dependent resistor and that of a thermistor?
As the light falling on an LDR gets brighter, the resistance decreases but 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 pds = 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 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 is the equation for current?
Current (A) = Charge in coulombs(C) / Time (s)
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Name two equations involving power?
Power = voltage X Current. Power = current2 X resistance.
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Name an equation involving energy, voltage, current and time?
Energy = Voltage X Current X time
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Name all of the prefixes.
Look at the prefix sheet.
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What is direct current and alternating current?
Dc passes around the circuit in one direction (cells and batteries) whilst a.c. passes in one direction then reverses and passes in the other direction (mains electricity).
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What are the key components of mains circuits?
Frequency in UK = 50 Hz (changes direction 50 times a second). “Voltage” = 230V. Has a live wire with a.c. with peak voltage of +325V and -325V. Direct pd equivalent of 230V.
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What is the equation for the frequency?
Frequency(Hz) = 1 / Time (s)
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Why is the cover of a three pin plug made of plastic and the pins 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 book
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What is the difference between a two-core plug and a three core plug?
A three core has Earth, Neutral and live wire whilst a two core plug doesn’t have an earth wire because they are used in appliances with plastic cases (double insulation) as the plastic is an insulator and can’t become live.
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What is a circuit breaker?
This can be used in the place of a fuse and is an electromagnetic switch that opens and cuts off the supply if the current is bigger than a certain value.
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Why do appliances with metal cases need to be earthed?
Because, if a fault develops and the live wire touches the case, the case becomes live and could give a shock to anyone who touches it.
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Why is a fuse always fitted in 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 higher than the normal working current?
Because if it is not, than the fuse will melt as soon as the appliance is switched on, but if it is much higher, then the fuse will not melt soon enough.
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What is a Residual current circuit breaker (RCCB)?
This cuts off the current in the live wire if it is different to the current in the neutral wire and works faster than a fuse or an ordinary circuit breaker.
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What is power and what is the equation linking power, energy transferred and time?
Power is the rate at which an appliance transfers electrical energy into other forms of energy. Power (W) = Energy transferred (J) / Time (s)
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What happens to electrical energy when charge flows through an appliance?
Electrical energy is transferred into other forms. In a resistor, electrical energy is transferred to the resistor so the resistor becomes hotter.
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Why are electrical faults dangerous?
As they can cause electric shocks and fires.
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Other cards in this set

Card 2

Front

Compare what happens to two objects that have opposite or the same charges are brought together.

Back

Opposites attract and objects with the same charge repel each other. The bigger the distance between the objects the weaker the force between them

Card 3

Front

What are ammeters and voltmeters?

Back

Preview of the front of card 3

Card 4

Front

What is resistance?

Back

Preview of the front of card 4

Card 5

Front

Which equation relates potential difference, work done and charge?

Back

Preview of the front of card 5
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