Current, potential difference and resistance (2.1) (R) Flashcards
What is the symbol for a switch (open and closed)?
What is the symbol for a cell and battery?
What is the symbol for a diode?
What is the symbol for a resistor?
What is the symbol for a variable resistor?
What is the symbol for a LED?
What is the symbol for a lamp?
What is the symbol for a fuse?
What is the symbol for a voltmeter?
What is the symbol for an ammeter?
What is the symbol for a thermistor?
What is the symbol for an LDR?
What must the circuit include for electrical charge to flow through a closed circuit?
a source of potential difference
What is electrical current?
a flow of electrical charge
What is the size of the electric current?
the rate of flow of electrical charge
A current has the (…) value at (…) point in a (…) closed loop
same
any
single
current is not used up
2 things
What does the current through a component depend on?
Both the resistance of the component and the potential difference across the component
The greater the resistance of the component the (…) the current for a given potential difference (pd) across the component.
smaller
Describe a method to investigate how changing the length of the wire affects its resistance.
- Connect the circuit as shown in the diagram attached.
- Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
- Record the reading on the ammeter** and on the **voltmeter.
- Move one of the crocodile clips closer until they are 90 cm apart.
- Record the new readings on the ammeter and the voltmeter.
- Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
- Use the results to calculate the resistance of each length of wire by using R = V/I, where R is resistance, V is voltage and I is current.
- Plot a graph of resistance against length for the resistance wire.
How does the value of resistance depend on the current in different resistors?
In some resistors is the value of the resistance constant, whereas in others it can change as the current changes?
some are fixed resistors and some are variable resistors
What is Ohm’s law?
that the voltage across a conductor is directly proportional to the current flowing through it
Describe the current through an ohmic (fixed) conductor
The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.
obey ohm’s law
How would you describe the resistance of components such as lamps, diodes, thermistors and LDRs?
not constant
it changes with the current through the component
Describe the correlation between the resistance through a filament lamp and temperature
The resistance of a filament lamp increases as the temperature of the filament increases.
Describe the current through a diode
The current through a diode flows in one direction only
Describe the resistance of a diode in the reverse direction
The diode has a very high resistance in the reverse direction
up until a particular voltage, the current will remain 0, and then quickly increase at the value
What component does this graph represent the resistance of?
ohmic (fixed) resistor
What component does this graph represent the resistance of?
filament lamp
What component does this graph represent the resistance of?
diode
The resistance of a thermistor (…) as the temperature increases
decreases
What is the application of thermistors?
thermostats (and other temperature sensors)
The resistance of an LDR (…) as light intensity increases
decreases
used to detect light levels
What is an application of LDRs?
switching lights on when it gets dark
how street lamps work
Draw a circuit diagram with a cell, ammeter, voltmeter, and variable resistor
Describe a method to investigate the relationship between current and potential difference for a resistor, bulb and diode
- Connect the circuit as shown
- Ensure that the power supply is set to zero at the start.
- Record the reading on the voltmeter** and **ammeter.
- Use the variable resistor to alter the potential difference.
- Record the new readings on the voltmeter and ammeter.
- Repeat steps three to four, each time increasing the potential difference slightly.
- Reverse the power supply connections and repeat steps two to six.
- Plot a graph of current against potential difference for each component.
- Repeat the experiment but replace the fixed resistor with a bulb and then diode
What is the supply of circuits powered by batteries or cells
dc
Draw a graph for a thermisistor
low heat on left of x axis, high heat on right
Draw a graph for an LDR
dark on left of x axis, bright on right
What are conventional currents?
Current flows from the negative end of the cell to the positive end. However scientists always draw the current in the opposite direction (due to prior beliefs). We call this conventional currents.
