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25 Cards in this Set
- Front
- Back
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Potential Difference
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The electrical energy per unit charge changed into other forms of energy (heat, light, sound, motion) as current moves across a component. Measured in VOLTS
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How do you calculate the work needed to move an electrical charge,Q, across a voltage, V?
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W = VQ
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EMF
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Source of electrical energy / charge in a circuit. Measured in VOLTS.
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Define a Volt
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Volt = Joule / Coulomb.
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I-V Characteristic of a Light Emitting Diode (LED)
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Draw a sketch
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I-V Characteristic of a resistor at constant temperature
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Draw a sketch
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I-V characteristic of a filament lamp
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Draw a sketch
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Ohm's Law
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The electric current through a conductor is proportional to the voltage across it if physical conditions (i.e. temperature) remains constant.
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Explain how and why the resistivity of a metal changes with changing temperature.
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Resistivity will increase. An increase in temperature will increase random thermal vibrations making conduction more difficult.
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Explain how and why the resistivity of a semiconductor changes with changing temperature.
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Resistivity will decrease. An increase in temperature will bump more electrons into the conduction zone, making resistivity go down.
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How will doubling the diameter of a wire affect its resistance?
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The resistance will be decreased by a factor of 4.
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How will doubling the length of a wire affect its resistance?
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The resistance will increase by a factor of 2.
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How will the resistance of a NTC thermistor change with an increase in temperature?
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The NTC thermistor is a semiconductor, as temperature goes up, resistance goes down.
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Thermistor
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Draw circuit symbol
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Light Dependent Resistor (LDR)
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Draw circuit symbol.
As light level increases, resistance decreases. |
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Write the equation for a voltage divider and draw a sketch to illustrate the meaning.
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Vout = Vin (Rbottom/Rtotal)
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How does a fuse work as a safety device?
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If too much current is flowing through the fuse, it melts and breaks the circuit. Fuses are typically made of very thin wire.
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State Kirchoff's 1st law and explain what quantity is conserved.
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All the current flowing into a junction must equal the current flowing out of it. Conservation of charge.
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Drift velocity
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Velocity of conduction electrons towards the positive end of the conductor. Tend to be slow (mm/s).
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Describe the different between conductors, semiconductors, and insulators in terms of number density, n
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Conductors - n is very high
Semiconductors - n is intermediate. can be increased by adding impurities. Insulators - n is very low. Few or no conduction electrons. |
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Relation between current and drift velocity.
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I = Anev
A= cross sectional area n=number density e=electron's charge, v=drift velocity |
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State Kirchoff's second law and identify the conserved quantity.
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Sum of emfs around a circuit must equal the sum of potential differences. This is conservation of energy.
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What is meant by internal resistance?
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Resistance inherent in any EMF, since all materials will have some resistance.
Little r in EMF = V+ Ir |
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Terminal Potential Difference
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The PD from one terminal of the battery to the other. Smaller than EMF since battery has internal resistance.
V in EMF = V + Ir |
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Define "lost volts"
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The energy/charge lost due to an EMF's internal resistance.
Ir in EMF = V + Ir |
