ENERGY, POWER AND RESISTANCE Flashcards
Draw circuit symbol for diode
Check
Draw circuit symbol for battery
Check
Draw circuit symbol for variable resistor
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Draw circuit symbol for thermistor
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Draw circuit symbol for LDR
Check
Equation for resistance
R = V/I
Equaition for resistivity
R = (pl)/A
WHat is the main electricity supply?
230V
What is Ohm’s Law?
Current is directly proportional to potential difference
Draw I-V diagrams for a wire, lamp and diode.
Check
A metal obeys Ohm’s law. What is it known as?
An ohmic conductor
What is reflected by the gradient on a IV graph?
Resistance
Resistance increases. What happens to current?
Decreases
Why is filament lamo not an ohmic conductor?
More current - electrons drift quicker - more collisions with lattice - ions have higher vibrational energy - less electrons can pass through
What is forward bias direction?
The direction is which diodes allow current to flow
What is reverse bias direction?
The direction the diode does nto allow current
How does diodes stop current flowing in the wrong direction?
Has infinite resistance when current flow in incorrect way
What are properties of diodes?
robust, versitile, operate at low potentials, long working life
Name examples of where diodes (or LEDs) are used.
Traffic lights, on and off indicators on TV
What are the fuctions of thermistors and LDRs?
Designed to respond to external conditions.
What is the definition of e.m.f?
The amount of energy transferred from one form of energy to electrical energy per coloumb of charge when charge passes through a power supply
What is e.m.f equal to?
The amount of pd across the power supply/battery when there is no current
How can e.m.f be measured?
High-resistance voltmeter in parallel
What is the equation for e.m.f?
E = W / Q
What is the definition for potential difference?
The energy transfered per unit charge from electrical energy to another form of energy per coloumb of charge when charge passes through it.
What unit if V equal to?
JC^-1
Name for factors that effect resistance?
Material, length, cross-sectional area, temperature
If the corss-sectional area increases, what happens to the resistance?
Decreases
If the length of the wire decreases, what happens to the resistance?
Decreases
What unit is used for electricity bills and why?
Kilowatt-hour
We use millions of J per day, cost of 1J is miniscule - not suitable
When are electricity bills recorded?
Every 3 months
What does 1 kWh mean?
Enery transfered by 1kWh device in one hour
Convert 1kWh into Joules.
3.6*10^6
Is kWh a unit of power?
No, unit of energy
