The rechargeable batteries for a laptop computer need a much smaller voltage tha

Question

The rechargeable batteries for a laptop computer need a much smaller voltage than what a wall socket provides. Therefore, a transformer is plugged into the wall socket and produces the necessary voltage for charging the batteries. The batteries are rated at 9.0 V, and a current of 272 mA is used to charge them. The wall socket provides a voltage of 120 V.

(a) Determine the turns ratio of the transformer

Ns/Np =

(b) What is the current coming from the wall socket?
Ip =

(c) Find the average power delivered by the wall socket and the average power sent to the batteries.
Pp =
Ps =

Ns/Np =

Explanation / Answer

Since efficiency of transformer is notgiven, i assume that the tranformer is ideal.

   For an ideal transformer

   inputpower   =   output power

   VS /VP   =   NS /NP   =   IP /IS

   a.   NS /NP   =   VS /VP

                        =   9.0/ 120

                        =   3/ 40

                        =   0.075

   b.   IP /IS   =   VS /VP

     Current from the wallsocket   IP                =   0.075* IS

                                                         =   0.075* 272 mA

                                                         = 20.4 mA

   c.   Power delivered by wallsocket   PP   =   VP* IP

                                                                  =   120* 20.4 * 10-3

                                                                  =   2.448   W

         Powersupplied to thebattery   PS   =   VS* IS

                                                               =   9.0* 272 * 10-3

                                                               =   2.448   W

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.