G482 -- IV Characteristics

Question 1

What is the IV characteristics for a filament lamp?

Answer 1

• the filament wire not obey Ohm’s Law
• as voltage across filament wire increases, current through filament wire increases
• the temperature of the filament wire increases as current increases
• resistance of filament wire increases with increasing temperature

Question 2

What is the IV characteristics for a thermistor?

Answer 2

• the thermistor does not obey Ohm’s law
• as voltage across thermistor increases current through thermistor increases
• as current through thermistor increases the temperature of the thermistor increases
• as temperature of thermistor increases resistance of thermistor decreases

Question 3

What is the IV characteristics for a diode or LED?

Answer 3

• the LED does not obey Ohm’s law
• below 1.5 V LED has infinite resistance
• no current until V is greater than 1.5 V
• above 1.5 V LED resistance decreases and LED intensity increases with increasing voltage
• above 1.8 V current rises almost linearly with increase in voltage

Question 4

How does temperature effect the resistance of pure metal wire or resistor?

Answer 4

• resistance is constant

* this only applies for small changes in temperature.

Question 5

How does temperature of a filament lmao affect its resistance?

Answer 5

• resistance of filament wire increases with increasing temperature
• the temperature of the lamp increases as current increases
• increased ion vibrations and more frequent electron-ion collisions
• (resistance increases as T increases, almost constant at low T).

Question 6

How does temperature change affect the resistance of a thermistor?

Answer 6

• resistance of thermistor decreases with increasing temperature
• gradient steepest at low temperature
• larger changes in R at lower temperatures gives larger changes in I and V
• thermistor best used in circuit which require switching at low temperatures e.g. frost protection heater

Question 7

How does light intensity effect resistance of an LDR?

Answer 7

• resistance of LDR decreases with increasing light intensity
• gradient is steepest at low light intensity
• larger changes in R at lower light intensities gives greater changes in I and V
• smaller changes in R at higher light intensities
• LDR is best use in circuits which requires switching at low light intensities (eg nightlight)

Question 8

What is the IV characteristics for a resistor?

Answer 8

• the resistor obeys Ohm’s Law
• graph of current against voltage is a straight line through the origin
• (resistance is constant)
• the current through the resistor is proportional to the potential difference across it provided physical conditions such as temperature remain constant