A laptop computer adapter (charger) shown in the figure has the following power specifications/rating, input: 100 – 240V a.c., 50-60Hz, output: 19V, 3.5 Amps. d.c. Which of the following are the two main functions of this power adapter?Stepping down of the voltage, rectifying d.c. to a.c. Stepping up of the voltage, rectifying d.c. to a.c. Stepping down of the voltage, rectifying a.c. to d.c. Stepping up of the voltage, rectifying a.c. to d.c.

Clay is charging his laptop computer battery, which has an adapter rated at 22 V and 3.25 A. A full chargetakes 40 minutes. What electrical resistance does the adapter have? How much charge does the fully chargedlaptop battery contain? What is the power requirement of the adapter? How much energy is used to re-chargethe battery?

What three voltages are commonly provided by the power supply to the various components inside the computer?

Cables with higher ____________ draw more charging current.*resistanceinductancecapacitancevoltage

1Which of the following units may NOT be used as a measure of power transfer?Joules per second (J/s)Kilowatts (kW)Watts (W)Watts per second (W/s)2A filament bulb is labelled ‘2.5 V, 1.25 W’.  How much energy will be transferred to it when it is connected to a 2.5 V battery for one minute?2.5 J150 J75 J48 J3The power adaptor of a laptop charges a laptop battery at a potential difference of 20 V and a current of 4 A.  Calculate its power output.24 W80 W5 W0.2 W4An electric motor is connected to a power supply.  The potential difference across the motor is 12 V and the current flowing through it is 2 A.  How much energy is transferred to the motor in 30 seconds?180 J24 J720 J12 J5Electrical energy is dissipated from a high voltage power cable at a rate of 50 kW.  If the current flowing in the cable is 100 A, calculate its resistance.0.005 Ω5,000,000 Ω500 Ω5 Ω6Calculate the amount of energy which is transferred when a charge of 72 C flows through a 6 V battery.0.08 J12 J78 J432 J

Transformers are an essential part of the National Grid.  What are they used for?To convert electricity from from a.c. to d.c. and vice versaTo adjust the supply of electricity according to how much energy is needed at a given timeTo improve the efficiency with which electrical energy can be transmitted around the countryTo allow energy to be transferred from one energy store to another2What name is given to the type of transformer which allows for the potential difference (‘voltage’) at which electricity is delivered to be increased?A high voltage transformerA boost transformerA step-up transformerA jump-up transformer3A current of 0.5 kA is flowing through a cable of resistance 20 Ω.  Calculate the power dissipated in the cable.5 × 106 W10 W10 kW5 W4There is a potential difference of 250 V across an electrical cable.  Calculate the amount of energy dissipated in the cable when a current of 100 A flows through it for 10 seconds.25 J2.5 J25,000 J250,000 J5A high voltage power cable transmits electrical energy with an efficiency of 0.8.  If 2 × 107 W of electrical power is supplied to one end of the cable, how much is transmitted to the opposite end?1.6 × 109 W4 × 106 W2.5 × 107 W1.6 × 107 W