ecifc neat a n o 00c), delivers 5mA coftent to an mp3 player e l vers m A cufren

Question

ecifc neat a n o 00c), delivers 5mA coftent to an mp3 player e l vers m A cufrent to an mp or loh before nee ding re charged. The recharger maintains a potential d;fferen ce of 2.5oV úcrost the ba ttery and charges with current So o mA for 1.oo hr to re charge the battery a) Find the Percentage of energi put nto the battery that is realited to play the musre p lay er. b) What form of energy did the difference between aput and ause fvl" ovtpvt of energy take? c) the battery is perfectly cnsolated, how much would its temperature rise in one fll cqcle of charge and discharge?

Explanation / Answer

a) The energy dessipate in the mp3 player is_

Eo = V.I.t (V=1.5volt; I= 5mA= 5×10-3 A and t=10 hr= 10×3600 Sec)

Eo = 1.5×5×10-3×10×3600

= 270 Joule.

Again the energy deliver to the battery by the charger is_

Ei = V.I.t (V= 2.5 volt; I= 50mA= 50×10-3 A and t= 1hr=3600 sec)

= 2.5×50×10-3×3600

= 450 Joule.

Thus the percentage of energy realised by the mp3 player is= (Eo/Ei)×100%

=(270/450)×100%

= 60%

b) The difference in input and output energy is converted into heat in the battery.

c) If the temparature rise of the battery is to C then_

m.s.t=(Ei - Eo) ( where m= 20gm= 0.02 kg; s=1000J/kg.degC)

0.02×1000×t= 450 - 270

t = 180/20

t= 9o C

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