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 Work, energy and power Questions

1.  Given that a lamp is rated 45W 240V. Calculate the resistance of the heating element.  

2.  An electric bulb is rated 40W, 240V. What is the resistance of its filament?

3.  An electrical immersion heater is rated 3kW, 250V. Choose a suitable fuse from 3A, 5A, 10A,

12A, and 20A that can be used in such an appliance.

4.  An electric kettle is rated 3KW, 250V. Determine the resistance of the coil

5.  An electric kettle rated 3.0Kw, 240V is filled with water. If the water boiled after 8 minutes

 of heating, determine the energy used in boiling the water.  

6.  (a) An electrical heater is rated 3.45KW. The heater is immersed in 2.4kg of water.

Calculate the minimum time it takes for the temperature of the water to rise from

23.0oC to 69.0oC. (Specific heat capacity of water = 4.2Jg-1K-1)  

 

Work, energy and power Answers

1.  D = 1V P I2R

 I = P R = P

  V I2

 = 45
1 mk = 45

ecolebooks.com

  240 (0.1875)2
1 mk

 

 = 0.1875A = 45  = 1280
1 mk

  0.03515

2.   P = V2

  R

 R = (240)2

40

= 1440

3. P = I

V

    3000 = 12A

250

suitable fuse 13A

4.  An electric kettle is rated 3KW, 250V. Determine the resistance of the coil

P = IV   = V2

R

300 = 2502

R

R = 62500

3000

= 20.83

Image From EcoleBooks.com5.  Energy E1 = Power x time

Image From EcoleBooks.com = 3000 x 8 x 60

= 1440000J

 

 

6.  = 2.4 x 4.2Jg-1K-1 x 46K (1mk)

= 2.4 x 4200JKg-1 K-1 x 46K (1mk)

= 463 6805J    

 Let the rime be t

  Energy H = Pt = 3450W x t

3450t = 463 680J

t = 134.4s  

 

 


 




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EcoleBooks | Work, energy and power Questions And Answers (part 2)

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