Physics Question

Test Preparation SAT Preparation
1

<p>I'd like to have an explanation for this one:</p>

<p>Q. An experimenter adds thermal energy to a block of some solid substance, but the temperature of the substance does not change. Which of the following explains this effect?</p>

<p>I. The thermal energy is used in a phase transformation.
II. The thermal energy increases the entropy of the substance.
III. The thermal energy is lost because heat engines can never be perfectly efficient.</p>

<p>(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I and III only</p>

<p>Thank you!</p>

2

<p>Think of the solid substance as something familiar – say ice.</p>

<p>As you add energy to ice (say by heating it) it eventually reaches 0 degrees centigrade while remaining a solid (i.e. ice). Then if you add still more energy it begins to liquify and at first results in water at temperature 0 centigrade. The energy goes into changing the phase – from solid to liquid.</p>

<p>The energy required (per unit mass) in the phase transition solid to liquid is the latent heat (of fusion).</p>

<p>Entropy is a measure of disorder. It is not relevant in the scenario descibed.</p>

<p>A heat engine describes a mechanism for converting thermal energy to mechanical energy. It is not relevant in the scenario described.</p>

<p>So (A).</p>

3

<p>Also, how come the answer to the following is C? Convex mirrors can make real images, too.</p>

<p>Q. Which of the following statements about mirrors are true for concave mirrors but not convex mirrors?</p>

<p>I. The focal point is in front of the mirror.
II. The image is real.
III. Incoming rays that hit the vertex are reflected at an equal angle to the axis.</p>

<p>(A) I only
(B) II only
(C) I and II only
(D) I and III only
(E) I, II, and III</p>

4

<p>Your assertion that convex mirrors can make real images is not true.</p>

<p>See any elementary physics books – perhaps the one that you’ve used in your high school physics course. </p>

<p>Or try a review book such as Princeton Review.</p>

<p>Or try a web search. See for example:</p>

<p>[Image</a> Characteristics for Convex Mirrors](<a href=“The Physics Classroom Website”>Physics Tutorial: Image Characteristics for Convex Mirrors)</p>

<p>Both your posts indicate that you need to review some physics basics.</p>

5

<p>When I was doing the first question, I chose A, too. However, the correct ans was marked as D, and I got this message. “A is not the correct answer. You should have selected D.”
I guess it’s a misprint or something. Thanks!</p>