Chung Cheng High School (Main) Sec 2 Physics 2014

\Chapter 13: Electrical Systems Name: ( ) Class: 2 _______ Date:

13.2 Effects of Electricity

1. Materials which are used as heating elements in electrical cookers and electrical irons should havea) A high melting point and low electrical resistanceb) A low melting point and high electrical resistancec) A high melting point and high electrical resistanced) A low melting point and low electrical resistance ( c )

2. What is a solenoid?a) Type of magnetic compass.b) Coil of wirec) Simple electric motor.d) Meter for measuring resistance ( b )

3. Which one of these electrical devices does not use electromagnet?a) Electric motorb) Electric door bellc) Electric light bulbd) Loudspeaker ( c )

4. When an electrical current passes through a conducting liquid, a chemical reaction occurs. This is called

a) Electrocutionb) Electroplatingc) Electrolyted) Electrolysis ( d )

5. Which of the following setups would coat the spoon with a layer of silver successfully?

( C )

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Chung Cheng High School (Main) Sec 2 Physics 2014

Structured Questions

6. An electric styrofoam cutter makes use of a hot wire to cut or “melt” styrofoam board into various shapes and sizes. Explain why the wire needs to be of high resistance?

A high resistance in the wires will allow more electrical energy to be converted to heat energy, thus the wire can melt the styrofoam board easily.

7. The temperature of the water flowing out of an instant heater can be increased by adjusting its temperature knob from low to high. Describe what happens to the resistance of the water heater when the knob is turned.

When the knob is turned from low to high, the resistance is increased as this converts more electrical energy to heat energy to heat up the water.

8. State an advantage of using an electromagnet in a crane, instead of a permanent magnet.

The magnetism of the electromagnet can be turned on or off by switching the circuit on or off.

9. In a Science practical lesson, the teacher demonstrated the chemical effect of electricity through electroplating. The diagram below shows the set-up to carry out electroplating. An iron spoon and a silver bar, used as the electrodes, are dipped into a solution.

(a) Explain why the surface of the spoon became more shiny when an electric current was passed through the solution.

The positively charged silver ions (Ag+) are attracted to the negatively-charged metal spoon. Hence, the spoon becomes more shiny. (Note: spoon is attached to the negative pole of the cell and the silver electrode to the positive pole).

Solution

Silver electrodeSpoon to be electroplated

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Chung Cheng High School (Main) Sec 2 Physics 2014

(c) A student stated that if the iron spoon is replaced with a plastic spoon, the plastic spoon would also be silver-plated. Is the student correct? Support your answer with an explanation. [2]

The student is wrong. Plastic spoon is a non-conductor of electricity (or insulator). Hence, it will not be negatively-charged if it is positioned at the same terminal as the metal spoon.

10. With the aid of diagrams below, explain how electric bell work.

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When the switch is on, the electromagnet will magnetis ed and attracts the iron block. As a result, the hammer will hit the gong and the circuit breaks. Thus the electromagnet demagnetizes and the hammer goes back to its original position. The cycle repeats itself and the bell rings continuously.