***November 2013 - Physics***

Test Preparation SAT Subject Test Preparation
121

<p>I vaguely remember doing this in chem 2 years ago. Since it’s clearly between 25 and 26 cm, you take the middle of the two numbers and do +/- from there. And it has to be +/- .2 not .01 because if the ruler or whatever only goes to the ones place, you can only approximate from the tenths place.</p>

<p>Also, it just doesn’t make sense to do plus or MINUS from 25 cm or PLUS or minus from 26 cm. You can clearly see it’s above 25 cm and below 26 cm. But, maybe I’m wrong to eliminate those choices because of that.</p>

<p>I’m about 75% sure about this. Anyone have any thoughts about this explanation?</p>

122

<p>@mbomb99
i think that the mirror answer was 10.5, because the question was how far is adult from a virtual image of a child. since adult was 7m away and child was 3.5m away from the mirror, the image of child is 10.5m away from the adult.</p>

<p>i also chose the answer 26cm +/- 1cm on the ruler question, but i really do not know if that is the correct answer.</p>

123

<p>What was the answer to the question with the Wire and a positively charged particle moving to the left</p>

124

<p>^ I think I chose the option that the charge moved away from the wire.</p>

125

<p>@PieOfApples This was my reasoning exactly. YOU CANT do .01 it would be too much of an approximation,
@humberthumbert you cant say 26±1 cm because it kinda explicitly makes it clear its under 26… sorry lol
@mbomb99 see @bla2501’s reasoning</p>

126

<p>What did you put for the lightbulb question?
Conduction, convection, radiation</p>

127

<p>radiation only i think? i mean, it said it was on an insulator, so conduction can’t happen. and there was some reason it wasn’t convection… was it in a vacuum?</p>

128

<p>yeah it was radiation only</p>

129

<p>the answer was 10.5 because the child was 7m away from his image and the guy is 3.5 meters behind the child so just add the 2 distances. simple</p>

130

<p>Yeah, 6 wrong 0 omitted is an 800. Not 100% sure though.</p>

<p>I forgot what the question was asking, but if it’s asking for the distance between fringes or the length of the fringes, I’m pretty sure wavelength AND hole size matter.</p>

131

<p>@pineOfApples distance does matter</p>

132

<p>Wait isn’t that what I said? If the question is about the distance, then both of the two factors matter. Or are you saying that one answer was distance? In that case yes.</p>

<p>I really don’t remember that question very well, sorry.</p>

133

<p>@pineOfApples you were right and so was I. both factors matter.</p>

134

<p>about the lightbulb question?
Conduction, convection, radiation
I think it’s radiation and convection, no conduction for sure, but won’t convection also affect the whole?</p>

135

<p>^ I thought it is convection and radiation too</p>

136

<p>^it cannot include convection because a fluid medium was absent around the source of heat.</p>

137

<p>I think the size went up and wavelength went up</p>

138

<p>I thought it was just radiation. Barron’s made that clear enough for me :slight_smile: Unless I’m wrong…</p>

139

<p>For the fringes question, I thought that increasing the wavelength and increasing the distance from the hole to the thing increases the distance between central fringe</p>

<p>the equation is x=(lambda)l/d
where x=distance from central fringe
d=slit size</p>

140

<p>I don’t think that question about the length of a ruler 25.5± whatever was about using “common sense”. I believe it to be about understanding the conventions of Modern Physics. Typically the uncertainty would be Half of the smallest scaled division which is half of 1 cm…= 0.5cm. But that was not an option so we had to choose the next best thing which is 25±1 cm…because we know that the typical uncertainty is AT LEAST 0.5. So the answer must be anything either equal to or above 0.5. We can’t assume 0.2 or 0.1 or whatever because that cannot be proved, and SAT doesn’t work with assumptions.</p>