Chapter 4 Electric Circuits Flashcards
What is electric current
The flow of electrical charge
What is a cell (description + description of photo)
Provides the ‘push’ for electrons in a circuit
- + and - with two lines of separate length
What is an ammeter (description + description of photo)
Used to measure current
-circle with A
What is a voltmeter (description + description of photo)
Used to measure the potential difference (voltage)
- circle with V
What’s a lamp (description + description of photo)
Emits light when current passes through it
-circle with cross
Whats a ldr (description + description of photo)
Light dependant resistor
- circle with rectangle and 2 arrows top left
What’s a fuse (description + description of photo)
Melts + breaks circuit if current is too high
-rectangle with line going through it
What’s a resistor (description + description of photo)
Limits current in a circuit
-rectangle
What’s a LED
Emits light when current passes through it
- circle with line going through it with play button with two arrows top right from angle
What’s a switch (description + description of photo)
Enables current in a circuit to be switched in or off
-one line,small circle line up - gap - small circle,small line ( open) - full line with two small circles (closed)
What’s a thermistor (description + description of photo)
Temperature dependant resistor
-rectangle with line from bottom right flat then change angle to top right
What’s a variable resistor (description + description of photo)
Allows current to be varied
-Rectangle with diagonal line from bottom left to top right
What sub atomic particle carry’s electric charge and where do they transfer energy
Millions of electrons - from the power source to the components in the circuit.
How to measure electrical current
I = Q / T
Current (amps) = charge (coulomb) / time (seconds)
What is potential difference
P.d. is the amount of work done (energy transferred) by each coulomb of charge that passes through the circuit between two points.
How to measure potential difference
V = E / Q
Potential difference (voltage) = energy (j) / charge (coulombs)
What is resistance
the opposistion to the flow of charge. Resistance is measured in a unit called ohms
4 factors that affect the resistance in a wire
- Length of wire
- Heat/temparature
- Type of material/Conductivity
- Diameter/cross sectional area of wire
What is ohms law
The current through a resistor at constant temperature is directly proportional to the Potential difference across the resistor.
How to measure potential difference with resistance
V = I x R
Potential difference (voltage) = current (Amps) X resistance (ohms)
How does current vary with voltage
As potential difference (voltage) increases current increases - directly proportional
Method of investigating Investigate whether a resistor, lamp and diode follow Ohm’s Law
- Collect equipment listed.
- Set up circuit as shown.
- Insert the component to be tested into the circuit.
- Set the variable resistor to maximum and turn on the switch
- Record the current on the ammeter and the voltage on the voltmeter
- Move the slider on the variable resistor to four more positions and repeat
step 5. - Repeat the experiment with other components
Equipment - • Cell
• Variable resistor
• Wires
• Ammeter
• Voltmeter
• Switch
• Resistor
• Filament Lamp
• Diode
How/are different components are proportional (resistor,filament lamp,diode)
P.d across resistor is directly proportional to the current in the resistor.The resistance of the resistor is constant
The potential difference across a filament lamp is not directly proportional to the current through resistor
A filament lamp does not obey ohms law and so can be described as a non - ohmic component. The resistance of a filament lamp is not a constant
The current is not directly proportional to the potential difference. The resistance changes as the current changes. A diode is a non ohmic conductor
I-V characteristics Rp method
- Set up the circuit as shown with the fixed resistor
- Vary the voltage across the component by changing the resistance of the variable resistor, using a wide
range of voltages (between 8-10 readings). Check the appropriate voltage reading on the voltmeter - For each voltage, record the value of the current from the ammeter 3 times and calculate the average
current - Increase the voltage further in steps of 0.5 V and repeat steps 2 and 3
- Make sure to switch off the circuit in between readings to prevent heating of the component and wires
- Reverse the terminals of the power supply and take readings for the negative voltage (and therefore
negative current) - Plot a graph of average current against voltage (an I–V graph) for each component
