PHSC 101 Final Exam

Which of the following statements is correct?

Moving electrons constitute electric currents.

A magnet does not exert a force on

a stationary electric charge

Heat transfer by conduction occurs

in liquids, solids, and gases.

The first law of thermodynamics is the same as the

law of conservation of energy

Heat transfer by convection occurs

only in liquids and gases

Sublimation refers to

the vaporization of a solid without first becoming a liquid

The current in a 20-ohm electric heater operated at 240 V is

12 A

A heat engine absorbs heat at 127°C and exhausts heat at 77°C. Its maximum efficiency is

13 percent

A 400-kg concrete block is 1 m long, 0.6 m wide, and 0.3 m high. It can exert three different pressures on a horizontal surface, depending on which face it rests on. The highest pressure is

13.1 kPa

An electric iron draws a current of 15 A when connected to a 120-V power source. Its resistance is

8 ohms

The specific heat of water is 4.2 kJ/kg°C. How long will it take for a 2-kW heating element to raise the temperature of 30 kg of water from 20°C to 80°C?

84 min

A current-carrying wire is in a magnetic field with the direction of the current perpendicular to that of the field.

The wire tends to move perpendicular to the field

Direct electric current cannot be used to operate

Transformers

The pressure at the bottom of a barrel filled with liquid does not depend on the

area of the liquid surface

A drawing of the field lines of a magnetic field provides information on

both the direction and the strength of the field

Radiation is emitted

by liquids, solids, and gases

Which of the following quantities is independent of the size and shape of an object composed of a given material?

density

The entropy of a system is a measure of its

disorder

Atoms and molecules are normally

electrically neutral

A kilowatt hour is a unit of

energy

Suppose there were molecules that had no attraction whatsoever for one another. A collection of such molecules would form a

gas

Molecules are, in general, farthest apart from one another in

gases

Ohm's law

holds only for metals

Ice floats in water because

its density is less than that of water

A charge of +Q attracts a charge of -Q 1 cm away with a force of F. Another charge of +Q is placed next to the first one. The force on the charge of -Q is now

2F

Fifty kJ of heat is added to a 10-kg piece of lead at its melting point of 330°C and 2 kg of lead melts. The heat of fusion of lead is

25 kJ/kg

Heat transfer in a vacuum

can take place only by radiation.

The conventional unit of battery capacity is the ampere-hour, which is actually a unit of

electric charge.

Relative to the electric force between two protons, the gravitational force between them is

weaker

Which of the following formulas expresses the relationship between the pressure and absolute temperature of a gas sample whose volume is fixed?

P1/T1=P2/T2

The specific heat of water is 4.2 kJ/kg°C. The heat needed to warm 8 kg of water from 20°C to 70°C is

1680 kJ.

The pressure on 100 liters of helium is increased from 100 kPa to 400 kPa. The new volume of the helium is

25 liters

The density of brass is 8 × 103 kg/m3. The volume occupied by 320 g of brass is

38 cm3

The primary coil of a transformer has 200 turns and its secondary coil has 40 turns. If the current in the secondary coil is 25 A, the current in the primary coil is

5 A

Three 12-V batteries cannot be connected to give a voltage for the set of

6 V

The power rating of an electric motor that draws a current of 3 A when operated at 240 V is

720 W

Ethanol boils at 172°F. The Celsius equivalent of this temperature is

78°C

The primary coil of a transformer is connected to a source of alternating current of voltage V. The voltage of the secondary current is

Any of these choices could be correct, depending on the ratio of turns in the transformer coils.

When heat is added to a body of matter, the resulting temperature increase does not depend upon

Its shape

Coulomb's formula F = KQ1Q2 /R2 gives the force between two charges in free space. The value of K

is the same under all circumstances

An object has a positive electric charge whenever

it has a deficiency of electrons

A thermometer calibrated in the Celsius scale and a thermometer calibrated in the Fahrenheit scale are used to measure the same temperature. The numerical reading on the Fahrenheit thermometer

may be smaller or larger than that on the Celsius thermometer.

Electric charge

occurs only in separate parcels of ±1.6 × 10-19 C.

A molecule that has lost an electron becomes a

positive ion

The volt is the unit of electric

potential difference

A sample of a gas is expanded to twice its original volume while its temperature is held constant. Relative to their original average energy, the new average energy of the

the same

Of the substances below, the one with the highest specific heat is

water