topic 2 - electricity Flashcards
What must be included for electrical charge to flow through a closed circuit?
a source of potential difference must be included
What is electric current?
the rate of flow of electrical charge
State the equation linking charge, current and time
Q = IT
charge = current x time
What is the value of current at any point in a single closed loop?
current is the same at all points in a closed loop
what two factors does the current in a circuit depend on?
- potential difference
- resistance
what occurs to the current when the resistance increases?
- the greater the resistance the smaller the current for a given potential difference across the component
What equation should be used to calculate the potential difference if current and resistance are known?
potential difference = current x resistance
V = IR
What is a zero error?
- reading on a measuring instrument when the value should be zero
- this is a systematic error. We cannot reduce it by carrying repeats
What is an “Ohmic Conductor”? State the condition required
- A conductor for which current and potential difference are directly proportional
- Resistance remains constant as current changes
- Temperature must be constant
How does the resistance change with the current?
- As current increases, electrons have more energy
- when electrons flow through a resistor, they collide with the atoms in the resistor
- this transfers energy to the atoms, causing them to vibrate more
- this makes it more difficult for electrons to flow through the resistor
-> so as the current increases, the resistance decreases
How does the resistance change with temperature
- in hotter temperatures, the thermistors resistance decreases
How does the resistance change with length?
- the greater the length, the greater the resistance and the lower the current
- electrons have to make their way through more resistor atoms, so it is harder than using a shorter wire
How does the resistance change with light?
- the greater the intensity of light, the lower the LDR’s resistance
- so the resistance is greatest when it is dark
How does the resistance of a diode change with voltage?
- diode allows current to flow freely in one direction
- in the opposite direction, it has a very high resistance so no current can flow
Give two examples of when a thermistor may be used
- in a thermostat to turn a heater on below a certain temperature
- in a freezer to turn on a cooler when the temperature becomes too high
What is an application for an LDR?
- street lights often use LDRs
- When light levels become too low, the light gains sufficient current to turn on
what are the two ways that a component can be connected in a circuit?
- series (same loop)
- parallel (adjacent loop)
state the rules for current, p.d., and resistance in a series circuit
- the current is the same through each component
- the total potential difference of the power supply is shared between the components
- the total resistance of two components is the sum of the resistance of each component
When two resistors are connected in series, how can u calculate the total resistance?
Rtotal = R1 +R2
Explain why in a series circuit, if one bulb goes out all of them will get out.
- An electron will pass through every component on its way around the circuit.
- If one of the bulbs is broken then current will not be able to flow round the circuit
- If one bulb goes out, they all go out
What happens to the resistance of a parallel circuit when another resistor is added in parallel?
- the resistance decreases
State the rules of current, potential difference and resistance in parallel circuits
- the p.d across each component is the same
- the total current through the whole circuit is the sum of the currents through the separate components
- the total resistance of two resistors is less than the resistance of the smallest individual resistor
Describe the current in a series circuit
In a series circuit, the current is the same at all positions since the charge only has one path to flow through
Describe the current in a parallel circuit
- In a parallel circuit, the current is shared between the different branches.
- When the charge reaches a junction it splits