Solve problems in DC circuits
Give 3 examples of series connected loads
- Cells/Batteries - Photovoltaic cells - Voltage divider circuits
What is the SI unit for current, resistance and power?
Amperes, ohms and watts
Name this meter
Analogue ammeter
What is a conductor?
Anything that allows electrons (electricity) to move easily through with little opposition/resistance
What is the relationship between temp and resistance of a positive temperature coefficient (PTC) thermistor ?
As temperature increases the resistance increases
What is the relationship between temp and resistance of a negative temperature coefficient (NTC) thermistor ?
As the temperature increases the resistance decreases
What is this symbol?
Fuse
What is the name of this resistor?
Grid resistor
What are 2 common uses for thermistors ?
Motor protection Temperature sensing
What is the name of this meter?
Multimeter
Where do you find the protons, neutrons and electrons in an atom and what are their electric charges ?
Neutrons in the nucleus - no charge Protons in the nucleus - positive charge Electrons orbit the nucleus - negative charge
What makes up a basic fuel cell?
Two electrodes immersed in a conductive liquid
What are the three ohms law equations?
V = IR I = V/R R = V/I
What is the name of this resistor?
Varistor
What's an application for a potentiometer?
Volume control on audio equipment
What meter is connected in series and parallel?
Wattmeter
What meter is used to measure power in a circuit ?
Wattmeter
What is a positive temperature coefficient? (PTC)
When a rise in temperature increase the resistance of the conductor
What is an open circuit?
When there is a break in the circuit
What is the name of this resistor?
Wire wound variable resistor
What is the name of this resistor?
Wire-wound resistor
When an open circuit occurs in a a parallel circuit the total current will...?
be reduced (how much depends on where the open is)
When an open circuit occurs in a parallel circuit the resistance will... ?
increase
How does electromagnetic induction work?
relative movement between a magnet and a conductor within a magnetic field produces electromotive force (electricity)
When a short circuit occurs in a parallel circuit what happens to the total circuit resistance?
resistance is reduced to almost zero
What is this resistors value?
2M ohms 5%
If 4 series connected batteries have a terminal voltage of 1.5v what is the total output voltage?
4 x 1.5 = 6volts
What is this resistors value?
5.6k ohms 5%
What is a short circuit ?
A connection between two conductors that should normally be insulated from one another.
What is the name of this resistor?
Carbon composite resistor
What is the name of this resistor?
Carbon film variable resistor
What is the name of this resistor?
Carbon-film resistor
What are the two dissimilar metals (electrodes) in a basic cell called ?
Cathode (negative electrode) Anode (positive electrode)
What is this symbol?
Circuit breaker
How do you measure voltage across a component?
Connect a voltmeter in parallel
How do you measure current in a component?
Connect an ammeter in series
If an open circuit occurs in a series circuit what happens to the current and resistance of the circuit
Current - can no longer flow so (drops to zero) Resistance - becomes infinite
How do you calculate current in series?
Current in any part of a series circuit will be the same
Name this meter
Digital volt meter
What is an insulator?
Does not allow electrons to move easily through, high opposition/resistance
What is current?
Electrical flow in a conductor
What's voltage?
Electrical pressure (potential)
How is an ammeter connected in a circuit?
In series
What happens to current in a parallel circuit?
It splits at each junction according to the resistance of each path
What are four factors affecting resistance?
Length Cross sectional area (CSA) Material Temperature
How does length affect resistance?
Length increase, resistance increase Length decrease, resistance decrease
What is the name of this resistor?
Light dependant resistor
What is a common use for light dependant resistors (LDR's) ?
Lighting control systems.
What is the relationship between the light dependant resistor and light?
Not exposed to light = very high resistance Exposed to light = very low resistance
Name three testers for resistance
Ohmmeter Insulation resistance tester Multimeter
What is a common use for metal oxide varistors?
Overvoltage protection devices
What are the three equations to work out power?
P = VI P = (I squared) x R P = (V squared) x R
How is a voltmeter connected in a circuit? (Series/parallel)
Parallel
What is it called when and emf is produced by light striking the surface of a photosensitive material?
Photoelectric effect
What is it called when an emf is produced by mechanical pressure being applied to a crystal?
Piezoelectric effect
Does copper have a positive or negative temperature coefficient ?
Positive
What type of connection is this?
Potentiometer
How do you work out the power losses in a system?
Power input minus power output
How do you workout the efficiency of a system/motor?
Power output divided by power input multiplied by 100
What is this symbol?
Power supply
If a short circuit occurs in a series circuit what happens to the resistance and current?
Resistance - reduced Current - increase
What type of connection is this?
Rheostat
How to work out total circuit resistance in a parallel circuit :
Rt = 1/((1/R1)+(1/R2))
Examples of parallel circuits:
Socket outlets Current divider circuits Lights
What happens when a short circuit occurs?
Total resistance is reduced Total current increases In most cases the increased current will trip a protection device
Provide an example of a series-parallel circuit:
Supply through an rcd then to 2 socket outlets in parallel
What is the thermocouple effect?
The production of an end when a temperature differential is created at the junction between two dissimilar metals
How to calculate total circuit voltage?
The sum of all individual voltages is the total
How to work out total circuit current
The sum of each branch's current
How to calculate resistance in series?
The sum of the individual resistances is the total resistance
How to work out Total circuit voltage in a parallel circuit ?
The total circuit voltage is the same across each component
What is the name of this resistor ?
Thermistor
What is the purpose of a rheostat?
To provide current adjustment
What is the purpose of a potentiometer?
To provide voltage adjustment
What happens when an open circuit occurs?
Total resistance becomes infinite and the load current drops to zero.