Mandatory Experiments: Electricity Flashcards
ME 1: To investigate variation of current with potential difference for filaments bulb, conductor, diode, copper sulfate solution: How was the potential difference changed throughout the experiment? Name the device used to vary p.d.? Graph.
Moving the sliding contact on the rheostat
Potential divider
Current on y-axis and voltage on x-axis
ME 1: To investigate variation of current with potential difference for filaments bulb, conductor, diode, copper sulfate solution: Does the graph verify Ohm’s law. What happens if inert electrodes are used in electrolyte experiment? Why does the resistance of filament bulb not remain constant? (4) What was observed in the electrolyte experiment as the current flowed?
Filament Bulb-not a straight line through the origin, no
Conductor-straight line through the origin, yes
Electrolyte with active electrodes-straight line through the origin, yes
If inert electrodes still straight line but not through origin. Does not verify Ohm’s law.
The filament increases in temperature causing vibration of the metal atoms which makes it harder for current to flow, increasing resistance.
Copper deposited on the cathode.
ME 2: Investigate variation of the resistance of a thermistor, conductor with temperature: How was resistance measured? How was temperature varied? Explain the two graphs. Why is the thermistor/conductor placed in glycerol instead of water? Graph axis?
Ohmmeter.
Bunsen burner.
Conductor: resistance increases linearly with temperature. As temperature increases the vibration of the atoms makes it harder for electrons to flow.
Thermistor: Resistance decreases exponentially with temperature. As temperature increases, free electrons and holes created exponentially and therefore increasing conductivity and reducing resistance.
Oil is a better conductor of heat.
Resistance on y-axis and rise in temperature on x-axis
ME 3: To measure resistivity of a wire: Name the equipment used to measure (a) the diameter (b) the length (c) the resistance? How did we know the wire was uniform? Describe how the data was collected?
Micrometer, metre stick, ohmmeter.
Measured the diameter at several locations and found an average value.
Make sure wire is straight and taut. Then measure distance between points with a metre stick where resistance is being measured with ohmmeter. Repeat for different lengths and values of resistance.
Check the micrometer for zero error. Place the wire between the grips of the micrometer. Tighten grip with slip control and read main + vernier scale.
Calculate an average value for diameter.
ME 3: To measure resistivity of a wire: Calculate resistivity from slope. How would resistivity of a fixed length of wire change if it’s diameter was doubled? Repeated on a warm day what were the effects of this?
resistivity = slope x cross-sectional area.
Resistance would be four times smaller.
Higher temperature = higher resistance
Higher temperature = increase in diameter
ME 4: Experiment to verify Joule’s Law: State Joule’s Law. Why was a fixed mass of water used? What precautions were taken? Graph adjustments.
The rate of conversion of electrical energy to heat is proportional to the current squared.
Rise in temperature depends on mass of water, can’t have a third variable.
Fixed time interval for current flowing and fixed mass of water.
Check and correct ammeter for any zero error.
Rise in temperature on y-axis and current squared on x-axis.
ME 4: Experiment to verify Joule’s Law: Does graph verify? Formula to calculate resistance. using graph estimate temperature at a given current.
Straight line through the origin verifys that (rise in temperature is proportional to Current squared)
slope = Rt / mc
Square the current given then read corresponding temperature from graph and add initial temperature.
ME 5: To investigate current with voltage for a semiconductor dioide: What happened when the junction voltage was exceeded for the semiconductor diode? How is the circuit changed for reverse bias? Does either graph verify Ohm’s law.
Current could flow as depletion layer broke down.
Polarity of battery switched
Milliammeter replaced by microammeter
Voltmeter put accros microammeter and diode (not just diode)
Protective resistor removed
Forward + Reverse: No not straight line through origin.
