Physics 010 Midterm #2

Transcription

1 Physics 010 Midterm #2 Thursday April 2, 8:30 10:00am This midterm is closed book. No books or notes allowed. Calculators are allowed There are 10 questions on this midterm, with marks noted beside each question. At the back of this midterm there is a formula and data sheet Write your answers in the exam booklet provided. You can use your second exam booklet for rough work. Put your name and student number on your exam booklet when finished Aaron and Terry are happy to clarify questions for you, but we cannot help you answer them!

2 Electrostatics (choose 2 or 3) 1. You want to determine if an object is neutral, positively charged, or negatively charged. You have another object known to be positively charged, and another object known to be negatively charged to use for this testing. How do you determine what charge your object has? 2. In the figure below, the grounding wire is removed first, followed by the rod, and the sphere is left with a positive charge. If the rod were removed first, followed by the grounding wire, would the sphere be left with a charge? Justify your answer 3. A metallic object is given a positive charge by the process of induction, as illustrated in the figure above. (a) Does the mass of the object increase, decrease, or remain the same? Why? (b) What happens to the mass of the object if it is given a positive charge by conduction?

3 4. There are four balls A, B, C, and D, each held by a non conducting thread. Ball A is negatively charged but you don't know whether balls B, C, and D are neutral or charged. The following interactions are observed between the four balls: B, C, and D are all attracted to A B and C have no effect on each other B and C are both attracted to D Say whether balls B, C, and D are negatively charged, positively charged, or neutral. Justify your answers. Series/Parallel Circuits (choose 2 or 3) 1. (a) What happens to the brightness of a bulb connected to a battery if another identical bulb is added to it in series? (b) What happens to the brightness of the first bulb if the second bulb is added to it in parallel? 2. (a) Ohm's Law is I = V R Explain what I, V, and R represent, and why Ohm's law makes sense. (b) Calculate the current in a series circuit with a 6V battery and two resistors each 1.5 ohms ( ). 3. (a) Which remains the same for a 10 and a 20 resistor connected in series with a battery: voltage or current? (b) What if the two resistors are connected in parallel with a battery?

4 Magnetism (choose 2 or 3) 1. (a) What kind of materials are magnetic and why? (b) Will either pole of a magnet attract a paper clip? Explain what is happening inside the attracted paper clip. 2. (a) How does an electromagnet (a coil of wire wrapped around a nail, and connected to a battery) produce a magnetic field? What factors determine how strong the magnetic field is? (b) Will the electromagnet work if you replace the nail with a wooden pencil? Explain why or why not. 3. You have two bars of iron, one a permanent magnet, and the other unmagnetized, which are identical otherwise. (a) Using a third bar of iron, known to be a permanent magnet, how can you determine which of the above two bars is magnetic, and which is not? (b) Can you determine the identities of the two bars if you use a third bar of iron which is not magnetized?

5 Reflection (choose 2 or 3) 1. Using the diagram below, sketch the image formed by the plane (flat) mirror of the object placed in front of the mirror, as seen by the eye. Is the image real or virtual? Is the image right side up or upside down? Is the image smaller, larger, or the same size as the object? 2. In the figure below, a woman is standing in front of a plane mirror. What is the minimum mirror height necessary for her to see her full image? Hint: try sketching rays leaving the woman's feet.

6 3. Hewitt, pg 553, exercise #3: Her eye at point P looks into the mirror. Which of the numbered cards can she see reflected in the mirror? (see the figure there) 4. Hewitt, pg. 554, # (a) Explain what total internal reflection is, and how it happens (b) Give one application of total internal reflection Refraction (choose 2 or 3) 1. (a) Why does light refract or bend when it goes from one material into a different material? (b) What determines the size of the refracted angle 2? (there will be a figure showing an incident ray and refracted ray). In this example, is material 2 less dense or more dense than material 1? 2. In the figure below, use ray tracing to show the image formed by the lens to the right of the lens, of the object (the arrow) which is on the left side of the lens (there will be a diagram like that in Assignment 5). Is the image real or virtual? Is the image right side up or upside down? Is the image larger, smaller, or the same size as the object/ 3. Consider an image formed of an object by a converging lens, as shown in the figure below (similar figure to that for #2). (a) What happens to the image if the top half of the object is covered? (b) What happens to the image if the top half of the lens is covered? Explain in each case.

7 4. (a) If, while standing on a bank, you wish to spear a fish beneath the water surface in front of you, should you aim above, below, or directly at the observed fish to make a direct hit? (b) If, instead, you zap the fish with a laser, should you aim above, below, or directly at the observed fish? Justify your answers.