Effect of an electric current on substances: Electrical conduction

5.0 Effect of an electric current on substances

5.1 Electrical conduction

Matter consists of electrical charges (negative (-) and positive (+)) because of the electrons and protons in it. But conduction of electricity depends on whether these charges are free to move about in the structure. Study Figure 5.1(a).

Questions 5.1(a)

1. Identify from A to E, the structures that conduct electricity.

2. For each structure identified in Question 1, explain why it conducts electricity.

3. For any one structure that does not conduct electricity, explain why it does not.

Answers to Questions 5.1(a)

Metals and graphite, whether solid or molten, have electrons which move about freely. In addition, ionic compounds in molten state or aqueous solutions have ions which move about freely. Therefore, they all conduct electricity. Non-metals and covalent compounds do not conduct electricity because they consist of neutral particles.

How do charges move naturally?

Natural movement of electrons in metals and graphite is similar to the random movement of molecules in liquids and gases. It occurs in all directions. The same behavior applies to ions in molten state or aqueous solutions of ionic compounds. But what is useful to us, as electrical energy, is movement that occurs in one direction.

How can we cause electrons and ions to flow in one direction?

Just like pressure difference is needed for air to flow in one direction (wind), we need electric potential difference (Voltage) for charges to move in one direction. This is provided by an electric cell (Figure 5.1(b)) or a battery of them.

Definitions

Study Figure 5.1(b) which shows how an electric cell is connected in a circuit to drive charges.

Electric Cell: The source of electricity. It drives electrons and negative ions in one direction.

Electrodes: Conductors connected to the negative or positive pole (end) of the electric cell.

Anode: The electrode connected to the positive pole of the cell. It is positive.

Cathode: The electrode connected to the negative pole of the cell. It is negative.

Anions: Negative ions (anode ions; i.e. ions attracted to the anode)

Cations: Positive ions (cathode ions; i.e. ions attracted to the cathode)

Circuit: The path along which electrical charges flow.

NB: Charges flow only when the circuit (path) is a complete loop. The red loop shown in Figure 5.1(b) assumes that the circuit is complete.

Electrodes are ordinary metals or graphite. They become anode or cathode when connected to the cell.

Questions 5.1(b)

Study Figure 5.1(b) above then answer the following questions.

1. Suggest why an electric bulb is used. What can replace the bulb?

2. P is an electrically charged particle. To which electrode will P move if it is positively charged?

3. Solid electrodes conduct electricity by use of electrons. In which direction do electrons move in the circuit when completed: clockwise or anticlockwise?

4. Name at least five (5) solid conductors of electricity.

Answers to Questions 5.1(b)

Substances which conduct electricity in solid state, also conduct electricity in molten state. They are elements with metallic structures, specifically metals and graphite. We can use this fact to identify metals and metallic structures.