Electrical Resistance Flashcards
What happens to a metal wire at a constant temperature when the voltage across it is varied?
The resistance does not change. Thus the current will be proportional to the volatage and a graph of current against voltage will be a straight line through the origin
How can you investigate the resistance of a component?
Connecting it to a power supply with an ammeter in series with it and a voltmeter parallel with it. A variable resistor can be connected in seies with the component so that the voltage across the component can be varied.
What is ohms law?
When the current and voltage are proportional because the resistance does not change as the voltage is increased
It applies to resistors
How will a component of low resistance appear on a current-voltage graph?
The gradient will be steeper (closer to the ground)
What happens to the resistance of a filament bulb as the voltage is raised?
It increases because the filament temperature increases substantially so it’s atoms will vibrate faster, have more collisions, making it harder for a current to flow.
Thus, if the voltage across a bulb is increased in equal steps, the resulting increases in current will become successively smaller and a graph of current against voltage will curve over.
What happens to the resistance of a silicon diode as the voltage is raised?
It drops so as the voltage increases the current will become successfully larger.
Thus if the voltage is increased in equal steps, the resulting increases in current will become successively larger and a graph of current against voltage will curve upwards (only after 0)
What happens to the resistance of a LDR as the voltage is raised?
In dark conditions LDRs contain few free electrons and so have a high resistance. However when light is shone on the electrons are freed and the resistance decreases. This is because it is made from semiconducting material.
What happens to the resistance of a thermistor as the voltage is raised?
At room temperature the number of free electrons is small so the resistance is large. When it is warmed the number of free electrons increases and the resistance decreases.
What is a resistor?
A component designed to control the current flowing in a circuit. A low resistance means a high current and vice-versa.
What is the relationship between voltage, current and resistance?
Voltage = current*resistance or V = I*R.
In what things are there both positive and negative ions? What are the ions called?
Electrolytic solutions and ionised gases Cations and anions
How does the resistance of a metal wire at a constant temperate change as the voltage across it is varied?
IT DOESN’T change. The resistance remains the same if it is at a constant temperature
What is the relationship between current and voltage in a circuit if the voltage is varied across the wire (at a constant temperature)? What is this relationship known as?
Current is proportional to voltage Ohm’s law
What would a current-voltage graph look like if it showed the resistance of a wire at a constant temperature? What does the gradient represent?
A straight line through the origin The gradient represents the resistance
What is the relationship between resistance, voltage and current?
Resistance = voltage/current
How does the resistance of a (filament) light bulb change as the voltage is varied and why?
The resistance increases because the temperature increases in the bulb. This happens because the moving electrons collide more with the metal ions causing resistance. As temperature increases they have more energy and therefore more collisions.
What would be the shape of a current-voltage graph for a bulb?
The line would have a steep gradient at first and then curve over.
What happens to the resistance of a semiconductor (silicon) diode as the voltage across it is varied?
The resistance drops.
What would the shape of a current-voltage graph look like for a semiconductors diode?
The line will be horizontal (0 current) until it curves upwards suddenly.
What is a resistor designed to do?
To control the amount of current flowing in a circuit.
What effect does the passage of electrical current have on conductors and why?
A heating effect is produced because electrons have kinetic energy which is passed to the atoms in the conductor as collisions occur.
What units is resistance measured in?
Ohms
How does an LDR operate?
The resistance drops as the light levels increase. It is made from semi-conducting material
Semi-conductors do not have many charge carriers initially (so the resistance is high), but more carriers are released when energy - in the form of light - falls on the material (and the resistance decreases)
The curent will increase a more light falls onto the LDR
How does a thermistor operate?
Resistance drops as temperature increases.
The current will increase as the temperature rises
What can be used to indicate the presence of current in a circuit?
Lamps and LEDs
How do diodes and LEDs utilise resistance?
Both diodes and LEDs only allow an electric current to pass in the direction of the arrow. In one direction they have a huge resistance to current and in the other, very little resistance. Diodes are used in power supplies for DC equipment.
What are LEDs?
Diodes that emit light as well as blocking current
What does the current in a series circuit depend on?
The applied voltage and the number and natures of other components
What is electric current in solid metallic conductors?
a flow of negatively charged electrons
