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P7: Quiz 6 – Answers
P7: Quiz 6 – Answers
1)
a)
a)
b) Temperature sensors
c)
c)
d)
i) Cold temperatures
ii) Hot temperatures
e) Any 2 from fire alarms, ovens, refrigerators, temperature sensors and automatic cooling fans in cars & buildings
2)
a)
i) Light Dependent Resistor
i) Cold temperatures
ii) Hot temperatures
e) Any 2 from fire alarms, ovens, refrigerators, temperature sensors and automatic cooling fans in cars & buildings
2)
a)
i) Light Dependent Resistor
b) Light sensors
c)
c)
d)
i) Dark conditions
ii) Light conditions
e) Any 2 from automatic lights (such as solar lights in your garden or streetlights), shutter speed sensors in cameras and burglar alarms
3)
a) When the surroundings are dark, the resistance of the LDR is very high, which means that the loop containing the LDR and bulb take a greater proportion of the source potential difference compared with the fixed resistor. A greater potential difference across the loop means a greater potential difference across the bulb. The brightness of the bulb is determined by power and we work out power by multiplying the current by the potential difference (P = IV). A greater potential difference across the bulb means that there is a greater power, thus resulting in the bulb getting brighter/ turning on. So, when the surroundings around the automatic light become dark, the bulb shines more brightly or turns on.
b) When the surroundings are light, the resistance of the LDR is very low, which means that the loop containing the LDR and bulb take a smaller proportion of the source potential difference. A smaller potential difference across the loop and bulb means that the power of the bulb is lower (P = IV). A smaller power means that the brightness of the light decreases. So, in light conditions, the brightness of the bulb decreases.
4)
a) In hot conditions, the resistance of the thermistor is low, which means that the thermistor takes a smaller proportion of the source potential difference, thus meaning that the potential difference in the loop containing the fixed resistor and cooling fan is quite high. A greater potential difference in the loop/ across the fan means that the fan will turn on/ move faster.
b) In cold conditions, the resistance of the thermistor is high, which means that the thermistor takes a greater proportion of the source potential difference, thus meaning that the potential difference in the loop is very low. A low potential difference in the loop/ across the fan means that the fan will be off/ move very slowly.
i) Dark conditions
ii) Light conditions
e) Any 2 from automatic lights (such as solar lights in your garden or streetlights), shutter speed sensors in cameras and burglar alarms
3)
a) When the surroundings are dark, the resistance of the LDR is very high, which means that the loop containing the LDR and bulb take a greater proportion of the source potential difference compared with the fixed resistor. A greater potential difference across the loop means a greater potential difference across the bulb. The brightness of the bulb is determined by power and we work out power by multiplying the current by the potential difference (P = IV). A greater potential difference across the bulb means that there is a greater power, thus resulting in the bulb getting brighter/ turning on. So, when the surroundings around the automatic light become dark, the bulb shines more brightly or turns on.
b) When the surroundings are light, the resistance of the LDR is very low, which means that the loop containing the LDR and bulb take a smaller proportion of the source potential difference. A smaller potential difference across the loop and bulb means that the power of the bulb is lower (P = IV). A smaller power means that the brightness of the light decreases. So, in light conditions, the brightness of the bulb decreases.
4)
a) In hot conditions, the resistance of the thermistor is low, which means that the thermistor takes a smaller proportion of the source potential difference, thus meaning that the potential difference in the loop containing the fixed resistor and cooling fan is quite high. A greater potential difference in the loop/ across the fan means that the fan will turn on/ move faster.
b) In cold conditions, the resistance of the thermistor is high, which means that the thermistor takes a greater proportion of the source potential difference, thus meaning that the potential difference in the loop is very low. A low potential difference in the loop/ across the fan means that the fan will be off/ move very slowly.
Questions
Click here for a printable PDF of the graphs and circuits in this quiz.
1)
a) Draw the symbol for a thermistor.
b) What are thermistors generally used as?
c) Use the graph below to show how the resistance of a thermistor changes as temperature increases.
Click here for a printable PDF of the graphs and circuits in this quiz.
1)
a) Draw the symbol for a thermistor.
b) What are thermistors generally used as?
c) Use the graph below to show how the resistance of a thermistor changes as temperature increases.
d)
i) Out of cold and hot temperatures, when is the resistance of a thermistor the highest?
ii) Out of cold and hot temperatures, when is the resistance of a thermistor the lowest?
e) Give two products that thermistors are used in.
2)
a)
i) What does LDR stand for?
ii) Draw the symbol for an LDR.
b) What are LDRs generally used as?
c) Use the graph below to show how the resistance of an LDR changes as light intensity increases.
i) Out of cold and hot temperatures, when is the resistance of a thermistor the highest?
ii) Out of cold and hot temperatures, when is the resistance of a thermistor the lowest?
e) Give two products that thermistors are used in.
2)
a)
i) What does LDR stand for?
ii) Draw the symbol for an LDR.
b) What are LDRs generally used as?
c) Use the graph below to show how the resistance of an LDR changes as light intensity increases.
d)
i) Out of dark and light conditions, when is the resistance of an LDR the highest?
ii) Out of dark and light conditions, when is the resistance of an LDR the lowest?
e) Give two products that LDRs are used in.
3) The circuit below is for an automatic light that turns on at night.
i) Out of dark and light conditions, when is the resistance of an LDR the highest?
ii) Out of dark and light conditions, when is the resistance of an LDR the lowest?
e) Give two products that LDRs are used in.
3) The circuit below is for an automatic light that turns on at night.
a) Explain why the light turns on/ is very bright in dark conditions.
b) Explain why the light turns off/ is very dim in light conditions.
4) The circuit below is used to control an automatic fan in a room. When the room is hot, the fan turns on. And when the room is cold, the fan turns off.
b) Explain why the light turns off/ is very dim in light conditions.
4) The circuit below is used to control an automatic fan in a room. When the room is hot, the fan turns on. And when the room is cold, the fan turns off.
a) Explain why the fan turns on when it is hot.
b) Explain why the fan turns off when it is cold.
b) Explain why the fan turns off when it is cold.