The resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The higher the resistance the more energy is required for current to flow through the conductor.
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Give the definition of resistance
potential difference across a component /current in it
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Give the equation for resistance
R of component= P.D across component / Current in component
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What is the unit of resistance
ohm (Ω), (after Georg Ohm)
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Define the ohm
The ohm (Ω) is defined as the resistance of a conductor when a constant potential difference of 1 volt applied, produces in the conductor a current of 1 ampere
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What is the base unit for ohmn
1 ohm = 1VA
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State Ohm's law
Ohms law states that for a metal kept at constant temperature, the current through the conductor is directly proportional to the voltage V across its ends.
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Explain the different in ohmic and non-ohmic conductors
Materials or objects where Ohm's law is true are called ohmic, whereas objects that do not obey Ohm's law are non-ohmic.
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Explain the I-V characteristic for resistors
1.V ∝ I 2 .Fixed resistors are ohmic conductors 3. Resistance is constant. 4. Resistance behaves the same wave regardless of polarities
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Explain the I-V characteristics for filament
1. Resistance is not constant, V is not proportional to I. 2. Non ohmic 3. Behaves the same way regardless of polarity
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Explain the shape of a filament lamp IV graph
.
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Explain what is meant by a thermistor
A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor
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Explain the I-V characteristic for thermistors
1. Voltage is not proportional to current, current increases with temperature 2. Non-ohmic 3. Resistance is not constant
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Explain why temperature leads to a drop in resistance
the numbder density of charge carriers increases so cu8rrent increases
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Explain what is meant by a diode
Diodes are electronic components which can be used to regulate the potential difference in circuits and to make logic gates.
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Explain why current can only flow in one direction in a diode
A diode has a very high (ideally infinite) resistance in one direction and a low (ideally zero) in the other. This means that current can only flow in the direction with low resistance.
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Explain the I-V characteristic for diode
1. current is not proportional to potential difference 2. non-ohmic conductor 3.. resistance is not constant
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State how resistance of an LDR changes with light intensity
Resistance decreases with increase in light intensity
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Explain how the resistance of an LDR is affected by low light levels
In the dark (low light levels), the resistance of an LDR is high and little current can flow through it.
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Explain how the resistance of an LDR is affected by bright light
In bright light, the resistance of an LDR is low and more current can flow through it.
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Explain why resistance decreases when light shines on an LDR
When light shines onto an LDR, the number density of charge carrier’s increases dramatically leading to a decrease in the resistance of the component
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Other cards in this set
Card 2
Front
Give the definition of resistance
Back
potential difference across a component /current in it
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