# What is an electric field? Sketch the shape of the electric field around a single proton.

Assignment 3 (CH. 7-9)

Chapter 7

Questions (use complete sentences)

1) What is an electric field? Sketch the shape of the electric field around a single proton.

2) If a uniform electric field is pointing east, what is the direction of the force on an electron? What is the direction of force on a positive particle?

3) If electrons are flowing counter clock wise in a circuit, which way is the conventional current flowing?

4) Explain what current, voltage, and resistance are?

5) Describe the differences between circuits with resistors connected in series vs. parallel.

1) Two charged particles exert an electrical force of 16 N on each other. What will the magnitude of the force be if the distance between them is reduced by half? What if the distance is doubled?

2) What would the separation between two particles each with a charge of 1 C have to be so that they each feel a force of 1 N.

3) A particle with a charge of 2.0 x 10-6 C experiences an upward force of 8N. What is the magnitude and direction of the electric field at that point? What if the charge was negative?

4) During 30 second of use, 250 C of charge flow through a microwave over. What is the current?

5) A current of 12 A flows through an electric heater operating on 120 V. What is the heater’s resistance?

6) The resistance of each brake light on an automobile is 6.6 Ω. Use the fact that cars have 12 V electrical systems to calculate the current that flows through each bulb.

7) An electric eel can generate a 400 V, 0.5 A shock for stunning its prey. What is the eel’s power output?

8) A clock consumes 2 W of electrical power. How much energy does it use each day?

Challenge (show work)

1) Three particles each with a charge of 2.5 x 10-6 C are located on the x-axis. There coordinates are (0,0), (2,0), and (6,0). What is the magnitude and direction of the electrical force on the particle located at (2,0)?

Chapter 8

Questions (use complete sentences)

1) Sketch the shape of the magnetic field around a bar magnet.

2) List the main type of electromagnetic waves in order of increasing frequency.

3) How does the radiation emitted by a black body change as its temperature increases?

4) What does a transformer do?

5) What are the three observations of magnetism talked about in class?

Problems (show work)

1) A cell phone charger is a transformer that reduces 120 V to 5V. For each 1,000 turns in the input coil, how many turns are there in the output coil?

2) What is the wavelength of a 60,000 Hz radio wave?

3) A transformer has an input coil of 2,000 turns, and an output coil of 500 turns. If 120 V is connected to the input coil how much voltage will it output?

4) Compute the frequency of an EM wave with a wavelength of 0.0542 m.

5) How much more energy would a black body radiate at 900 K vs 300 K?

6) What wavelength of light do humans mostly radiate if the human body temperature is 310 K?

Chapter 9

Questions (use complete sentences)

1) Describe how the path of a ray is deviated as it passes from one medium to another in which the speed of light is lower. Contrast this with the case when the speed of light in the second medium is higher.

2) A light ray in air enters a block of plastic as shown below. Which of the numbered paths is the correct one for the ray in the plastic?

3) What is total internal refection, and how is it related to the critical angle?

4) What is the difference between a converging and diverging lens?

1) A light ray traveling in air strikes the surface of a flat glass block at an angle of 50°. Part of the light is reflected and part is refracted. What are the angles of reflection and refraction?

2) Compute the index of refraction of (a) air, (b) benzene, and (c) crown glass.

3) A camera is equipped with a lens of 30 cm. When an object 200 cm away is being photographed, how far from the lens should the film be placed?

4) A 2 cm tall object stands in front of a converging lens. It is desired that a virtual image 2.5 times larger than the object be formed. How far form the lens must the object be placed to accomplish this task, if the final image is located 15 cm from the lens?

5) When viewed from a magnifying glass, a stamp that is 2 cm wide appears upright and 6 cm wide. What is the magnification?

6) A small object is placed to the left of a convex lens and on its optical axis. The object is 30 cm from the lens, which has a focal length of 10 cm. Determine the location of the image. Describe the image.

7) Solve number 6 again but replacing the convex lens with a diverging lens of focal length 10cm.

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