Describe Ohm's law, classify given materials into conductors and insulators, provide an example of a semiconductor, identify energy forms and transformations in a circuit, and explain alloys.

8.

e)

(i) Ohm's law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature and other physical conditions remain constant. Mathematically, $V = IR$.

(ii) Classification of materials:

• Air: Insulator
• Paper: Insulator
• Iron: Conductor
• Pure water: Insulator (or very poor conductor)
• Aluminium: Conductor
• Salt solution: Conductor
• Plastic: Insulator
• Lime juice: Conductor
• Glass: Insulator
• Stone: Insulator

(iii) One example of a semi-conductor: Silicon (or Germanium).

a)

(i) The form of energy in the battery is chemical energy.

(ii) The two forms of energy emitted by the filament bulb are light energy and heat energy.

(iii) The amount of energy in the battery decreases.

(iv) The energy transformation that takes place in the circuit is: Chemical energy $\to$ Electrical energy $\to$ Light energy + Heat energy.

b)

(i) An alloy is a mixture of two or more metals, or a metal and a non-metal, combined to enhance specific properties.

(ii) Two advantages of alloys:

• Alloys are often stronger and harder than their constituent pure metals.
• Alloys can be made more resistant to corrosion or rust.

(iii) Constituent elements of each alloy:
I. Brass: Copper and Zinc.
II. Stainless steel: Iron, Chromium, and Nickel (with a small amount of Carbon).

c)

(i) A hormone is a chemical substance produced by endocrine glands in the body, transported in the blood, and acts on target cells or organs to regulate specific physiological processes.

(ii) Hormone produced by each organ:
I. Pancreas: Insulin (or Glucagon).
II. Ovaries: Estrogen (or Progesterone).
III. Testes: Testosterone.

(iii) One effect of underproduction of each hormone:
I. Pancreas (Insulin): Underproduction leads to Diabetes mellitus, characterized by high blood glucose levels.
II. Ovaries (Estrogen): Underproduction can lead to irregular menstrual cycles, reduced development of secondary sexual characteristics, or infertility.
III. Testes (Testosterone): Underproduction can lead to reduced sperm production, decreased libido, or reduced development of male secondary sexual characteristics.

d)
Two reasons why ecological studies are important:

• They help us understand the interactions between living organisms and their environment, which is crucial for maintaining biodiversity.
• They provide knowledge necessary for conservation efforts and sustainable management of natural resources.

9.

a)

(i) Three advantages of using mercury as a thermometric substance over alcohol:

• Mercury has a wider temperature range (higher boiling point and lower freezing point) than alcohol.
• Mercury is a good conductor of heat, allowing it to respond quickly to temperature changes.
• Mercury is opaque and has a shiny surface, making it easily visible in a capillary tube.

(ii)