Exam 2 Physics

A typical metabolic rate while walking is

300 W

A Celsius thermometer and an absolute thermometer are used to measure the temperature of the same gas sample. The readings on the thermometers are respectively Tc and Tk. Which is correct?

Tc is smaller than Tk

Which of the following formulas relating temperatures on the Celsius and Fahrenheit scales is correct?

Tc=(5/9)(Tf-32*)

When the voltage across a certain resistance is V, the power delivered is P. If the voltage is doubled to V/2, the power delivered becomes

P/4

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

P1/T1=P2/T2

True or False: Moving electrons constitute electric currents.

TRUE

A magnet does not exert a force on

a stationary electric charge.

A magnet attracts

all metals.

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

area of the liquid surface, but does depend on liquid density, acceleration of gravity, and height of the liquid

When a current passes through a resistance, the electrical energy that is lost

becomes heat.

When a magnetized iron bar is strongly heated, its magnetic field

becomes weaker.

Ohm's law

holds only for metals.

Superconductivity occurs in certain substances

only at very low temperatures.

Heat transfer by conduction occurs

only in liquids and gases.

If undisturbed, an electric current in a superconducting wire loop

will continue indefinitely.

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?

63 minutes

True or False: A proton in an atom circulates around its nucleus.

FALSE

True or False: All protons have the same charge.

TRUE

True or False: Protons and electrons have charges equal in magnitude although opposite in sign.

TRUE

True or False: The proton mass is almost the same as the neutron mass.

TRUE

The electrons in an atom

are some distance away from the nucleus.

A barometer measures

atmospheric pressure

The freezing point of a substance is always lower than its

boiling point

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

both the direction and strength of the field.

Heat transfer in a vacuum

can take place only by radiation.

The properties of several different materials are being compared. If the samples all have the same volume, the one with the greatest mass also has the greatest

density

When a liquid becomes a vapor,

it must absorb heat.

Direct electric currents can not be used to operate

transformers

The voltage needed to produce a current of 8 A in a resistance of 12 ohms is

96 Volts

The watt, the unit of power, is equal to the

(volt)(ampere)

A temperature of 20*C is the same as

68*F

Which has the highest specific heat?

Water

Coulomb's formula F=KQ1Q2/R^2 gives the force between two separate charges in free space. The value of K

is the same under all circumstances.

When a liquid freezes to become a solid,

it gives off heat.

An object has a positive electric charge whenever

it has a deficiency of electrons.

Ice floats in water because

its density is less than that of water.

The temperature of a gas sample in a rigid container is reduced. The pressure the gas exerts on the container walls decreases because

its molecules have lower average speeds and so strike the walls less often with less momentum.

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

its shape.

A cake of soap is placed in a bathtub sink. The buoyant force on the soap is

less than its weight.

A compass needle tends to

line up parallel to a magnetic field.

A sample of 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 molecules is

the same.

Two charges of +Q attracts are 1 cm apart. If one of the charges is replaced by a charge of -Q, the magnitude of the force between them is

the same.

A negative electric charge

interacts with both positive and negative charges.

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

gas

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

lower than V, equal to V, or higher than V depending on the ratio of turns in the transformer coils.

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.

In order for an object to sink when placed in water, the object's average density must be

more than that of water.

The pressure on the bottom of an object inside a liquid is

more than the pressure on its top.

Electric charge

occurs only in separate parcels of +-1.6X10^-19C.

A current-carrying loop in a magnetic field always tends to turn until the plane of the loop is

parallel to the field.

A molecule that has lost an electron becomes a

positive ion.

The volt is the unit of electric

potential difference.

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

weaker.

True or False: Electrons carry electric currents.

FALSE

True or False: Protons are positively charged.

TRUE

When 90 kJ is removed from a 2-kg copper bar, its temperature drops from 200*C to 85*C. The specific heat of copper is

0.39 kJ/kg*C

The average pressure of the atmosphere at sea level corresponds to

101kPa and 15 lb/in^2

Two charges, one positive and the other negative, are initially 2 cm apart and are then pulled away from each other until they are 8cm apart. The force between them is now smaller by a factor of

16

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

Two charges repel each other with a force of 10^-6 N when they are 10 cm apart. When they are brought closer together until they are 2 cm apart, the force between them becomes

2.5X10^-5 N.

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

25 liters

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

2F.

The density of air is 1.3 kg/m^3. The air in a room 5 m long, 4 m wide, and 2.5 m high has a mass of

65 kg

A 400-kg concrete block is 1 m long, 0.6 m wide, and 0.3 m high. Its density is

667 kg/m

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

720 Watts.

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

78*C

True or False: Protons and electrons have equal masses.

FALSE

True or False: The motion of electrons produces electric currents.

FALSE

Which has the lowest specific heat?

Gold

True or False: The positive charge in an atomic nucleus is due to the protons it contains.

TRUE

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.

Which of the following is not true of molecular motion in a gas?

There is a definite average direction of motion at a given temperature.

The nucleus of an atom

contains most of the atom's mass.

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

density

A current is flowing south along a power line. Neglecting the earth's field, the direction of the magnetic field under the power line is

east.

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

electric charge.

Atoms and molecules are normally

electrically neutral.

A kilowatt hour is a unit of

energy

When a gas is forced into a smaller volume without a change in temperature, its pressure increases because its molecules

strike the container walls more often.

The current in a 24-W, 12-V light bulb is

2 Amperes

True or False: The proton mass is greater than the electron mass.

TRUE

The current with which a transformer is used

must be AC

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

gases.

The specific heat of ice is 2.1 kJ/kg*C. When 50 kJ of heat is removed from 2kg of ice initially at -5*C, the final temperature of the ice is

-17*C

At which of the following Celsius temperatures will a Fahrenheit thermometer show the same reading in degrees?

-40*C

Molecular motion in a gas is the minimum possible at

0 K

True or False: Electric currents are carried by conductors and insulators only.

FALSE