Electricity and Magnetism Review for Midterm Exam Answers 1. Note the following substances : 1. Rubber 2. Plastic 3. Aluminum 4. Copper 5. Steel Which of these substances are insulators? A) 1 and 2 B) 1 and 3 C) 2, 4 and 5 D) 3, 4 and 5 2. A manufacturer wants to wrap an electric wire with material that does not conduct electricity. Which one of the following materials CANNOT be used for this purpose? A) Ceramic C) Plastic B) Graphite D) Glass 3. Which of the following would increase the electrical conductivity of a circuit? 1- A thicker wire 2- A longer wire 3- A decrease in the temperature of the wire 4- The use of porcelain wire A) 1 and 2 C) 2 and 4 B) 1 and 3 D) 3 and 4
4. The circuit illustrated below consists of two resistors R 1 and R 2, an ammeter A and a power supply. The ammeter reads 0.5 A. The total resistance is 30. A R1 R2 V I = 0.5 A 10 Ω 20 Ω What voltage, V, would a voltmeter read if it was connected across the terminals of the power supply? A) 5 V C) 15 V B) 10 V D) 60 V 5. The heating element of an electric stove has a resistance of 50. It is connected to a power source of 220 V and turned on for 2.0 minutes. What is the current which flows through this heating element? A) 4.4 A B) 8.8 A C) 9.1 A D) 27.3 A Work:
6. While having breakfast, you notice the following information on the specification plate of the toaster: You also note that this toaster toasts the bread in 1.5 minutes. 120 V 6 A 60 Hz What quantity of electrical energy is consumed by the toaster's element to toast the bread? A) 720 J B) 1080 J C) 10 800 J D) 64 800 J Work: 7. During the summer, the 750-W electric motor of a swimming pool pump is used 24 hours a day for 100 days. Electricity costs $0.05/kW h. How much does it cost to use this motor during the summer? A) $3.75 C) $90.00 B) $37.50 D) $90 000.00 Work
8. A large circular saw is connected to a 220 V circuit. The current intensity is 25.0 A. How much energy does this machine consume in 1.00 hour? A) 1.98 10 7 J B) 3.17 10 4 J C) 5.50 10 3 J D) 8.18 10 2 J Work 9. A coffee maker is connected to a 120 V outlet. The resistance, R, of the heating element of the coffee maker is 20. This coffee maker stays on for 2 hours. How much energy is used by the heating element of the coffee maker during this period? A) 0.72 kj C) 86.4 kj B) 1.44 kj D) 5184 kj Work =
10. You are given five electrically charged spheres and told that sphere 4 is positively charged. The following diagrams show what happens to these spheres when they are suspended in pairs close to each other. 1 2 1 3 2 4 3 5 Which of these spheres is negatively charged? A) Sphere 1 C) Sphere 3 B) Sphere 2 D) Sphere 5
11. The following diagram shows a bar magnet and four compasses. Which compass shows the needle pointing in the correct direction? A) Compass 1 B) Compass 2 C) D) Compass 4 12. The following diagram shows a magnet, an electromagnet and a small car containing iron. S N + - What happens when an electric current flows through the electromagnet? Using the right hand rule for solenoids, you should discover that the south pole of the electromagnet is closest to the south pole of the bar magnet, therefore they will repel. The small car is made of iron and therefore ferromagnetic, so will be attracted by the electromagnet.
13. A battery operated toy police car has 3 types of lights that can come on in different ways. The car has only one electrical circuit that controls the lights The headlights and the tail lights come on when you start the car If necessary, the flashing light can come on at the same time as the headlights and the tail lights. This toy police car is illustrated in the diagram below: Draw the circuit diagram that represents the electrical circuit that can control the lights in this toy police car. headlights Tail lights Flashing lights
14. The electrical circuit of a magnetic alarm system is illustrated in the diagram below Identify the electrical function of the five components above. Component Name of Component Electrical Function 1 Magnetic switch Control 2 wires Conduction 3 Speakers/flashing lights Transformation of energy 4 Battery Power supply 5 fuse protection
15. Your parents currently have a 42 inch plasma tv that requires 120 V and 0.5 A of current. Your family typically watches 6 hours of tv per day. They are thinking of replacing their tv with a 50 inch LED which will consume about 348 per day based on the average usage. Your parents tell you that even though the tv is bigger, the energy consumption will decrease because LED tvs use much less energy. Are your parents correct? Does the 50 inch LED tv consume less energy than the 42 inch plasma tv? Show work. For the 42 inch plasma Your parents were correct, the 50 inch LED tv uses less energy than the 42 inch plasma based on your average daily consumption