electricity

• In the experiment to determine how the resistance of a thermistor varies with temperature, how can the student determine the resistance at each value of the temperature?


  Use R = V / I, measuring V from the voltmeter and I from the ammeter at that particular temperature of the water bath .
• Suggest a table that a student could draw when determining how the resistance of a thermistor varies with temperature.

  
• State the equipment needed for the experiment to determine how the resistance of a thermistor varies with temperature.

  Power supply, wires, water bath, ammeter, voltmeter, submersible thermistor, temperature.
• Suggest the IV, DV and control variables to determine how the resistance of a thermistor varies with temperature.

  IV: temperature, DV: Resistance, CVs: potential difference,
• In the experiment to determine how the resistance of a thermistor varies with temperature, what type of variable is the potential difference: independent, dependent or control?

  Control
• In the experiment to determine how the resistance of a thermistor varies with temperature, what type of variable is the temperature: independent, dependent or control?

  Independent
• In the experiment to determine how the resistance of a thermistor varies with temperature, what type of variable is the resistance: independent, dependent or control?

  Dependent
• Suggest how you can control the temperature of the thermistor in this experiment?

  Place a submersible thermistor in a beaker, and pour boiling water into the beaker until the thermistor is fully covered. As the water cools, measure the current and p.d. for every value of the temperature required for your experiment (e.g. every 5°C until room temperature).
• Draw a circuit that could be used to investigate the resistance of a thermistor.

  
• Sketch a graph of resistivity against light intensity for an LDR.

  
• Sketch a graph of resistivity against temperature for an NTC thermistor.

  
• Sketch a graph of resistance against light intensity for an LDR.

  
• Sketch a graph of resistance against temperature for an NTC thermistor.

  
• What is an LDR?

  An LDR is a resistor that has a resistance which decreases with light intensity.
• What is an NTC thermistor?

  An NTC thermistor is a resistor that has a resistance which decreases with temperature.
• What is a thermistor?

  A thermistor is a resistor that has a resistance which varies with temperature.
• Materials which are less conductive typically have ___________ charge carriers.

  Less
• Materials with lower resistivity typically have ___________ charge carriers.

  More
• Materials with less charge carriers have ___________ resistivity.

  Higher
• Materials with more charge carriers are ___________ at conducting electricity.

  Better
• What is the diameter of a 30cm nichrome wire with resistance 0.068 Ω? (Nichrome has a resistivity 1.50 x 10 ^ -8).


  0.29mm (to 2 s f)
• What is the length of an aluminium square rod with resistance 0.200Ω and width 2.00cm? (The resistivity of aluminium is 2.82 x 10^ -8 Ω m).

  2.84km (to 3 sf)
• What is the resistance of 80cm of a 0.50mm diameter copper wire? (The resistivity of copper is 1.7 x 10 ^ -8 Ω m).

  0.069 Ω (to 2 sf)
• What is the resistivity of a wire with diameter 0.30mm, length 20cm and resistance 3.0 Ω?

  1.1 x 10 ^ -6 Ω m (to 2 sf)
• The resistivity of a metal conductor decreases as the temperature _________.

  Decreases
• As temperature increases, the resistivity of a metal conductor __________.

  Increases
• Resistivity is independent of...

  The shape and size of the material.
• What 2 factors does resistivity depend on?

  The type of material and the temperature.
• The higher the resistivity of a material, the _________ conductive the material is.

  less
• Which material is more conductive, material A (ρ = 3.5 x 10^-5) or material B (ρ = 2.44 x 10^-8)? Why?

  Material B because it has a lower resistivity.
• The more better a material is at conducting electricity, the ___________ it's resistivity.

  lower
• Define resistivity

  
• State 3 formulae for electrical power in terms of V, I and R.

  P = I V, P = I^2 R, P = V^2 / R
• Draw a circuit that can be used to plot a graph of I against V for any component.

  
• How can you calculate the resistance of a component at a particular current given it's I-V graph?

  Draw a tangent to the curve at that current. The resistance is given by 1/gradient of that tangent.
• How can you calculate the resistance of a component at a particular potential difference given it's I-V graph?

  Draw a tangent to the curve at that potential difference. The resistance is given by 1/gradient of that tangent.
• What is an I-V graph?

  An I-V graph is a graph of current through a component against potential difference across a component.
• How does current vary with potential difference for an ohmic conductor?

  Current is directly proportional to potential difference, so as potential difference increases current also increases.
• How does potential difference vary with current for an ohmic conductor?

  Potential difference is directly proportional to current, so as current increases potential difference also increases.
• How does resistance vary with potential difference for an ohmic conductor?

  Resistance is constant for any potential difference in an ohmic conductor.