Friday, 5 September 2014

ELECTRICITY PROBLEMS AND QUESTIONS ON RESISTANCE, CURRENT & OHMS LAW


                                     Electricity 

1. Calculate the length of a copper wire of cross sectional area 0.8x10-7m2 that has a resistance of 2Ω.

2. Calculate the resistivity of a material if a 2.5 m length of wire of that material with a diameter of 0.3 mm has a resistance of 3Ω

3. Calculate the resistance between the large faces of a slab of germanium of thickness 1 mm and area 1.5 cm2.

4. Calculate the length of a eureka wire of diameter 0.8 mm that has a resistance of 8Ω

5. Calculate the current flowing in a copper wire of cross-sectional area 3x10-7m2 if the drift velocity is 0.2mms-1. 

6. Calculate the drift velocity in a silver wire of cross-sectional area 1.5x10-7m2 if a current of 25mA flows through it.

7. Calculate the current through the following resistors:
(a) 120Ω connected to 240V 
(b) 4700 Ω connected to 12V 
(c) 10kΩ connected to 6V 
(d) 2.5MΩ connected to 25V 

8. What is the resistance of the following?
(a) a lamp that draws 2A from a 12V supply 
(b) a kettle that draws 4A from a 240V supply 

9. The two lines on the graph in the diagram show a specimen of metal wire at two different temperatures. 
(a) calculate the resistance of the wire at each temperature 
(b) which line shows the higher temperature? 
(c) does the material disobey Ohm's Law? Explain your answer. 

Useful data:
Resistivity of copper = 1.69x10-8 Ωm
Resistivity of germanium = 0.65 Ωm
Resistivity of eureka = 47x10--8 Ωm
Resistivity of silver = 1.6x10-8 Ωm
Free electrons in copper = 1027 m-3
Electron charge = 1.6x10-19 C