Subject: conceptual4
From: Michele Gressman
Date: Tue, 27 Sep 2005 18:34:17 -0700 (PDT)
To: Larry Rudnick


1.

Correct An atom in an excited state contains more of what type of energy than the same atom in the ground state?

Your Answer:

electric potential energy
  Correct. The potential energy is electrical because it is based on the attraction of the positive nucleus to the negative electrons.

2.

Correct An atom which has 4 protons and 6 neutrons will be electrically neutral if it contains

Your Answer:

4 electrons.
  For an atom to be electrically neutral, the number of protons must be equal to the number of electrons.

3.

Correct At extremely high temperatures (e.g., millions of degrees), which of the following best describes the phase of matter?

Your Answer:

a plasma consisting of positively charged ions and free electrons
  Correct.

4.

Correct How much energy would be released if we could completely convert the mass of a 1 kilogram rock into energy?

Your Answer:

9 x 1016 joules
  We use the formula E = mc2. The mass is 1 kg, the speed of light squared is 9 x 1016 m2/s2. Multiplying, we get an answer of 9 x 1016 joules.

5.

Incorrect If an electron at level 1 in a hydrogen atom absorbs 10.2 eV of energy, it will move to level 2. What typically happens next?

Your Answer:

The electron remains in level 2 until it absorbs an additional 10.2 eV of energy.

Correct Answer:

The electron returns to level 1 by releasing 10.2 eV of energy.
  It will not simply wait in an excited state for something else to happen. (In the rare case where the additional energy were absorbed before the electron fell back to the ground state, this added energy would be enough to ionize it.)

6.

Incorrect Suppose an atom emits a photon of light. Which of the following must have occurred within the atom?

Your Answer:

An electron must have jumped from a lower energy level to a higher energy level.

Correct Answer:

An electron must have dropped from a higher energy level to a lower energy level.
  This would require the atom to gain energy, not lose it by emitting a photon.

7.

Incorrect Suppose you built a scale-model atom in which the nucleus is the size of a tennis ball. About how far would the cloud of electrons extend?

Your Answer:

a few meters

Correct Answer:

several kilometers
  Too small.

8.

Incorrect Suppose you had some molecular oxygen (O2) chilled enough so that it was in liquid form. Which of the following best describes the phase changes that would occur as you heated the liquid oxygen up?

Your Answer:

It would sublime into a gas, then the molecules would lose electrons until no electrons were left, then the molecules would dissociate into individual oxygen nuclei.

Correct Answer:

It would evaporate into a gas, then the molecules would dissociate into individual oxygen atoms, then the atoms would become increasingly ionized as you continued to raise the temperature.
  Liquids do not sublime, and molecules dissociate long before losing all their electrons.

9.

Incorrect Suppose you heat up an oven to 400 degrees F and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?

Your Answer:

The molecules in the water are moving faster than the molecules in the oven.

Correct Answer:

The water can transfer heat to your arm more quickly than the air.
  The boiling water has a lower temperature than the hot oven, which means the molecules are moving slower.

10.

Correct Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?

Your Answer:

The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.
  Correct.

11.

Correct When a rock is held above the ground, we say it has some potential energy. When we let it go, it falls and we say the potential energy is converted to kinetic energy. Finally, the rock hits the ground (and stays there). What has happened to the energy?

Your Answer:

The energy goes to producing sound and to heating the ground, rock and surrounding air.
  Correct.

12.

Incorrect When the returning Space Shuttle enters the atmosphere and begins to slow down, its kinetic energy is primarily converted into ________

Your Answer:

potential energy.

Correct Answer:

thermal energy.
  As it gets closer to the center of Earth, it loses, not gains, potential energy.

13.

Incorrect Which object has the most kinetic energy?

Your Answer:

a 2-ton truck moving 50 km/hr

Correct Answer:

a 1-ton car moving 100 km/hr
  Compared to the 1-ton car moving 100 km/hr, this has twice the mass but half the speed. Since kinetic energy depends on speed squared, this object has less kinetic energy that the car.

14.

Incorrect Which of the following is a form of electrical potential energy?

Your Answer:

light from a fluorescent bulb.

Correct Answer:

energy coming to your house from power companies.
  Energy from a light bulb is carried by light and hence is radiative energy.

15.

Incorrect Which of the following represent the smallest range of temperature?

Your Answer:

0 to 100 degrees Kelvin.

Correct Answer:

0 to 100 degrees Fahrenheit.
  A 100-degree range in Kelvin is greater than a 100-degree range in Fahrenheit.

16.

Incorrect Which of the following scenarios involves energy that we would typically calculate with Einstein's formula E=mc2?

Your Answer:

A mass raised to a great height has a lot of gravitational potential energy.

Correct Answer:

When hydrogen is fused into helium, whether in the Sun or a nuclear bomb, some of the mass disappears and becomes energy.
  Gravitational potential energy is not described by Einstein's formula.

17.

Incorrect Which of the following statements about electrons is NOT true?

Your Answer:

Electrons have very little mass compared to protons or neutrons.

Correct Answer:

Electrons orbit the nucleus rather like planets orbiting the Sun.
  This is true, but the question asked for a false statement.


__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com