P6 Electricity for Gadgets

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The higher the resistance, the ____ the current. The resistance of a length of wire depends on its length.
Lower
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How does a variable resistor work?
By changing the length of wire in the circuit; the longer the wire, the greater the resistance
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The steeper the gradient of a voltage-current graph, the ___ the resistance. The voltage-current graph for a resistor is a straight line passing through the origin, showing that voltage is directly proportional to current. The resistor obeys ___ ___
Greater; Ohms Law
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The resistance of a filament bulb increases as the current increases, not obeying Ohms law. When electrons collide with the atoms in the filament, it makes the atoms vibrate more. What does this increased vibration lead to?
A increased number of collisions so the resistance increases. An increase in the temperature of the filament.
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For a fixed resistor, the gradient of the graph is ___ to the resistance. The gradient of the voltage-current graph for a filament lamp increases as the _____ increases. So the resistance must be found using _______ ____ from the graph.
Equal: Resistance: Instantaneous values
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What two types of resistors could a potential divider circuit have?
Fixed. The output voltage is a fixed proportion of the supply voltage. OR Variable. The output vottage can be altered.
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What is threshold voltage?
The voltage needed to switch on a circuit.Using a variable resistor as one part of the potential divider allows the threshold voltage to be set.
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What can be done to decrease the total resistance of a resistor?
The resistors can be arranged parallel.
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The resistance of a light-dependent resistor (LDR) ____ as the light intensity increases. The resistance of a thermistor ____ as the temperature increases.
Decreases; Decreases.
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How is the behaviour of a thermistor different to a resistor?
Resistance of a thermistor decreases with temperature
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What is a thermistor?
An electronic device whose resistance changes with temperature.
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Street lights have LDRs in potential divider circuits. When it is dark, the resistance of the LDR is ___, the output voltage is ___ and switches on the street light. A thermistor can be used to switch on a heater when the _____ gets too low.
High; High; Temperature
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What is a transistor?
An electronic component used to amplify or switch electric signals. In a transistor, a small base current (flow of electrons in an electric circuit) can switch on a greater current through the collector.
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How does an OR gate behave?
Like two switches in parallel.
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A NAND gate behaves as if it is an AND gate followed by a ___ gate. A NOR gate behaves as if it is an OR gate followed by a ___ gate.
Not; Not
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What is a logic gate?
Electronic components that respond to signals by following preset logic rules.
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Switches, LDRs and thermistors are used in a potential divider circuit to make the input to a logic gate high. When the switch is ___, the logic gate is low. When the switch is ____, the input is connected directly to the voltage supply, input is ___
Open; Closed; High
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What happens if you use a variable resistor instead of a fixed resistor?
A threshold level can be set.
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Explain how a relay is used to switch on a heater
An output current from gate passes through an electromagnet, attracts an iron armature, this pivots and pushes an insulating bar against the contacts.
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Why is a relay needed to switch on a heater?
Output current from logic gate is too low to power heater and the higher current could damage the logic gate so the relay isolates it.
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Current output from logic gates is low but can be passed through a ____ to switch on a larger current needed for motors, heaters etc. It also isolates the logic circuit from the high current to avoid damage to the logic gates.
Relay
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How can the direction of a field around a wire be found?
Right-hand grip rule.
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What does Fleming's left-hand rule allow you to do?
To predict the direction in which a motor turns. The direction of the current, magnetic field and motion are all at right angles to each other.
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What three things can be done to make a motor spin faster?
Increase current; Increase number of turns on coil; Increase magnetic field strength.
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Motors have communicators. What is the job of the communicator?
Is to make the motor continue to spin and reverses the current in the coil every half turn. This makes sure the force on the coil is always in the same direction.
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What are slip rings used for in a AC generator?
The are connected to the ends of the coil to allow the coil to spin without winding the wire around itself. The brushes are contacts that touch the slip rings to complete the circuit.
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The size of the induced voltage depends on the rate at which the magnetic field changes: If the wire is moved slowly the voltage is ___. If the wire is moved quickly voltage is ___.
Low; Higher
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When the wire moves downwards of the magnet moves up, the induced voltage is _____ and the current is in the ____ direction.
Reversed; Opposite
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What is a transformer and what does it consist of?
Its a device which can change the voltage and the current of electricity. it consists of two coils of wire wound onto an iron core.
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The input AC voltage is connected to the ___ coil. The output AC voltage is obtained from the ____ coil. Step down transformers have more turns on their ___ coils. Step up have more on their ___ coils.
Primary; Secondary; Primary; Secondary
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The changing current in the primary coil produces a changing ____ _____ in the core. This induces a changing voltage in the secondary coil.
Magnetic Field.
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An isolating transformer has the same output voltage as the input voltage. Why use an isolating transformer as a shaving socket in the bathroom?
The output terminals are not live, there is no danger of electrocution if you touch the socket with wet hands.
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A diode consists of a piece of n-type semiconductor and a piece of p-type semiconductor joined together to form a junction. Use ideas about electrons to explain how a diode works
It forms a depletion layer. Depletion layer acts as an insulator. Voltage applied with positive to n-type depletion layer widens no current. VA with positive to p-type depletion layer narrows. By increasing the voltage,layer disappears+current passes
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When a DC supply is connected to a capacitor, the capacitor becomes ____. The voltage across the capacitor increases until it is ____ to the supply voltage.
Charged; Equal
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What is a diode?
A electronic component that only lets current pass through in one direction
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What voltage do most diodes need before they can start to work?
0.6V
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When a diode is connected so that a current passes, it is ___ biased. When a diode is connected so NO current passes, it is ____ biased.
Forward; Reverse
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A DC generator has a communicator. What part of an AC generator delivers a current to the brushes?
Via slip rings attached to the end of the coils.
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How can the voltage produced by a generator be increased?
Increase the no.of turns on the electromagnets, increase the magnetic field strength.
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Electricity is generated at 25kV and transmitted at 400kV. What difference will this make to the curret in the overheard cables and what effect will this have on the power?
Current is reduced to 1/16th of original value. The power loss will be 1/16th² of what it would have been
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Four diodes can be arranged to make a bridge circuit. The addition of a large capacitor makes the output ______.
Smoother
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Some garden lights can come automatically when it is dusk. What component is used in these lights to make it possible?
Light Dependent Resistor (LDR)
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What are the truth tables for an AND and OR gate?
AND OR
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What are the truth tables for an NAND and NOR gate?
NAND NOR
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Other cards in this set

Card 2

Front

How does a variable resistor work?

Back

By changing the length of wire in the circuit; the longer the wire, the greater the resistance

Card 3

Front

The steeper the gradient of a voltage-current graph, the ___ the resistance. The voltage-current graph for a resistor is a straight line passing through the origin, showing that voltage is directly proportional to current. The resistor obeys ___ ___

Back

Preview of the front of card 3

Card 4

Front

The resistance of a filament bulb increases as the current increases, not obeying Ohms law. When electrons collide with the atoms in the filament, it makes the atoms vibrate more. What does this increased vibration lead to?

Back

Preview of the front of card 4

Card 5

Front

For a fixed resistor, the gradient of the graph is ___ to the resistance. The gradient of the voltage-current graph for a filament lamp increases as the _____ increases. So the resistance must be found using _______ ____ from the graph.

Back

Preview of the front of card 5
View more cards

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