• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Biology; Chemistry; Physics: Post your doubts here!

L

luckywang

Messages
242
Reaction score
21
Points
18
help me on these?
describe the use of magnetic materials in audio/video tapes.
discuss the dating of objects by the use of 14C.
describe how the Geiger-Marsden alpha-particle scattering experiment provides evidence for th nuclear atom.
 
daredevil

daredevil

Messages
1,394
Reaction score
1,377
Points
173
Spidey21 said:
do you know how LDR and thermistor work?? :eek:
Click to expand...
ok u need to have a diagram of their circuits in front of u for this.
Thermistors:
thermistors are mostly used in potential divider circuits. in such a circuit there are two resistors with one on top and the other in bottom. the bottom one is connected to the output. the input voltage is constant. if the thermistor is placed on top and a fixed resistor is at the bottom then this happens: as temperature falls the resistance increases. the current is the same throughout the circuit bcuz it is a series circuit but voltage of the components is added up to give the input voltage. so in this case voltage of the thermistor increases as the temperature decreases so there is a higher voltage here than in the next resistor (the fixed resistor). this results in lower voltage in the fixed resistor. if the temperature increases, the opposite happens and the voltage of the fixed resistor (output voltage) increases. this is used in fire alarms.
thermistors can also be placed at the bottom with the fixed reisistor at the top. the same principle applies but this time take note of where the voltage changes and what affect tht haves on the output voltage(just like done previously)

LDRs:
light dependant resistors work in a similar way in a potential divider circuit. here resistance decreases as light intensity ncreases. apply the potential divider method and work it out. if u can't then tell me and i will try to ecplain *PHEW* :sick: :)
 
Spidey21

Spidey21

Messages
3,809
Reaction score
3,115
Points
273
daredevil said:
ok u need to have a diagram of their circuits in front of u for this.
Thermistors:
thermistors are mostly used in potential divider circuits. in such a circuit there are two resistors with one on top and the other in bottom. the bottom one is connected to the output. the input voltage is constant. if the thermistor is placed on top and a fixed resistor is at the bottom then this happens: as temperature falls the resistance increases. the current is the same throughout the circuit bcuz it is a series circuit but voltage of the components is added up to give the input voltage. so in this case voltage of the thermistor increases as the temperature decreases so there is a higher voltage here than in the next resistor (the fixed resistor). this results in lower voltage in the fixed resistor. if the temperature increases, the opposite happens and the voltage of the fixed resistor (output voltage) increases. this is used in fire alarms.
thermistors can also be placed at the bottom with the fixed reisistor at the top. the same principle applies but this time take note of where the voltage changes and what affect tht haves on the output voltage(just like done previously)

LDRs:
light dependant resistors work in a similar way in a potential divider circuit. here resistance decreases as light intensity ncreases. apply the potential divider method and work it out. if u can't then tell me and i will try to ecplain *PHEW* :sick: :)
Click to expand...
i know how they work i was just answering the guys question...:|
 
ISFSAT

ISFSAT

Messages
128
Reaction score
78
Points
38
Q: On a building site, metal scaffolding is firmly embedded in the damp ground. A builder holds a mains operated electric drill in one hand. With his other hand he holds on to the scaffolding. the power cable of the drill is damaged where it enters the metal casing of the drill. What danger does this present to the builder?
A. a current could pass through the builder and electrocute him.
B. a current in the scaffolding could heat it up and burn him
C. the large current could blow the fuse and damage the drill.
D. the large current could make the motor spin too quickly.
Q: Which reading is shown to the nearest mm?
A. 0.7m
B. 0.76m
C. 0.761m
D. 0.7614m
Help plz......:cautious:
 
syed1995

syed1995

Messages
1,824
Reaction score
949
Points
123
ISFSAT said:
Q: On a building site, metal scaffolding is firmly embedded in the damp ground. A builder holds a mains operated electric drill in one hand. With his other hand he holds on to the scaffolding. the power cable of the drill is damaged where it enters the metal casing of the drill. What danger does this present to the builder?
A. a current could pass through the builder and electrocute him.
B. a current in the scaffolding could heat it up and burn him
C. the large current could blow the fuse and damage the drill.
D. the large current could make the motor spin too quickly.
Q: Which reading is shown to the nearest mm?
A. 0.7m
B. 0.76m
C. 0.761m
D. 0.7614m
Help plz......:cautious:
Click to expand...


Q1. A ? well the power cable is touching the metal casing .. causing it to get live?

Q2. C for sure. 1mm = 1/1000 m.
 
syed1995

syed1995

Messages
1,824
Reaction score
949
Points
123
You must log in or register to reply here.
Top