EE Review Q3

An electric kettle was marked 500 W, 230 V found to take 15 minutes to bring 1 kilogram of water at 15°C to boiling point. Determine the heat efficiency of the kettle.

• 79.1%

• 75.3%

• 72.4%

• 74.8%

10¹³ ergs/sec is equal to how many kilowatts?

• 1,000

• 250

• 100

• 10

What is 1 kW-hr in BTU?

• 4,186

• 3,413

• 746

• 1,000

When heat is transferred into any other form of energy or when other forms of energy are converted into heat, the total amount of energy is constant. This is known as

• First law of thermodynamics

• Boyle’s law

• Specific heat

• Isothermal expansion

If a 220 V heater is used on 110 V supply, heat produced by it will be ____ as much

• one-half

• twice

• one-fourth

• four times

For a given line voltage, four heating coils will produce maximum heat when connected

• all in parallel

• all in series

• with two parallel pairs in series

• one pair in parallel with the other two in series

A force of 10,000 N accelerates a body to velocity 0.1 km/s. The power developed is ____ kW.

• 1,000,000

• 36,000

• 3600

• 1000

Two heaters A and B are in parallel across supply voltage V. Heater A produces 500 kcal in 20 minutes and B produces 1000 kcal in 10 minutes. The resistance of A is 10 ohms. What is the resistance of B, if the same heaters are connected in series voltage V?

• 4.5 ohms

• 2.5 ohms

• 4.5 ohms

• 0.14 ohm

In the SI system of units, the unit of force is

• kg-wt

• Newton

• Joule

• N-m

The SI unit of energy is

• Joule

• kWh

• kcal

• m-kg