مراجعة نهائية للامتحان في العلوم باللغة الإنجليزية للصف الثامن - الفصل الثالث

هيكلة الـــــــــــــعلــــــــــوم، Contents. Unit، Module

(3) Understanding Waves. M3: Information Technologies.

Lessons. L1: Communicating with Signals.

L2: Modern Communication with Digital

Signals

(4) Humans and their Place in the Universe.

M1: Earth and Human Activity.

M2: The Sun – Earth – Moon System.

M3: Exploring the Universe.

L1: Human Population Trends. L2: People and the Environment. L1: Earth’s Motion Around the Sun. L2: Lunar Phases. L3: Eclipses. L1: Gravity and the Universe. L2: The Solar System – ENRICHMENT.

written part LO – 1: Pages: 158, 159, 160 ,162. [Textbook, figures, investigations] Question (1) Explain how signals communicate information and list the process of transmitting signals from sender to receiver.

A signal is a piece of information that is communicated through using the senses.

Sharing Information: 1Vocal cords send information encoded in sound waves through the air.

2To read a page of text, you need a light source to reflect off the page in very specific patterns. Your brain interprets this as information encoded in text.

3Braille encodes information as arrangements of dots. You feel the dots to interpret them.

The process of transmitting signals includes: 1Encoding Signals (to put information in the form of a code). Morse code and binary are examples of ways to encode signals.

2Transmitting Signals: When you talk to another person, you are transmitting information. Signals can be transmitted long distances by using electromagnetic waves such as radio waves, microwaves, or light waves.

3Decoding a signal refers to the process of converting a received encoded or modulated signal back into its original form, making it intelligible or usable for its intended purpose.

Question (2) Explain how optical fibers transmit signals across distance.

[a] what are the components of the fiber optics? A thin strand of glass or plastic; cladding with a refraction index less than the core material.

[b] Explain how optical fibers transmit signals across distance.

Reflection: Optical fibers rely heavily on the principle of total internal reflection. Light is repeatedly reflected within the core of the fiber, allowing it to travel long distances with minimal loss.

Refraction: occurs at the interface between the core and the cladding. The difference in the refractive index between these two materials is what causes the light to undergo total internal reflection within the core.

Transmission: refers to the passage of light through the optical fiber. Optical fibers are designed to transmit light from one end to the other with minimal loss.

Short Answer: Because of total internal reflection, a beam of light can be transmitted within the fiber over a very long distance. Page 2 of 14

LO – 2: Pages: 176, 178, 181, 188. [Textbook, figures]

Question (3) Compare Analog signals and Digital signals and how they are affected with noise.

Analog Signal، Digital Signal

[1] Analog signals change

[1] A digital signal is not continuously changing

continuously over time

values like analog signals, instead they are

displayed by a discrete value.

Characteristics and Features

[2] They are represented by a continuous smooth curve.

[2] They are represented by a stepping pulse.

Examples

[3] Analog signals can have a range of values. Analog Clock, Radio signals.

[3] Digital signals can have two values: on (1) and off (0). Computer data, Telephone calls.

Representation

Interaction with Noise representation.

Noise is an unavoidable modification of a signal.

When noise is added to a digital signal, the information can still be clear to the receiver.

Interaction with Noise

When an analog signal is recorded, the noise is recorded along with the original signal. Over time, noise accumulates, and the information deteriorates.

A device that receives and translates a digital signal is only expecting one of the two values, on or off. Noise then is easily filtered off without significant deterioration to the original information even when transmitted over long distances.

This makes digitized signals a more reliable way to encode and transmit information than analog signals.

LO – 3: Pages: 10, 12, 22. [Textbook, figures, investigations] Compare human population growth around the world and list the factors that affect the health and growth of the human population. Question (1): Define Population? A population is all the members of a species living in a given area.

Question (2): How does the rate of human population growth from years 200 to 1800 compared to the rate of growth from 1800 to 2000?

Between 200 and 1800, the human population increased steadily at a slow rate. The human population between 1800 and 2000 rose sharply.

Question (3): list the factors that affect the health and growth of the human population. Improved health care, clean water, technological advancements, and birth rates and death rates

Question (4): Observe the graph showing the percent of youth and elderly in four countries. Use the data to predict how the population of each country will change. Country A: The population of this country will increase quickly because the number of youths greatly exceeds the number of elderly.

Country B: The population will increase slowly because the number of youths only exceeds the number of elderly by a small percentage.

Country C: This country will increase at a slower rate than Country B.

Country D: The population of this country will decrease because the number of elderly exceeds the number of youths.

Question (5): Some developing countries, such as India, are becoming more industrialized and are also increasing in population. Predict the effect that this might have on the carrying capacity of Earth. As developing countries become more industrialized, they increase their use of resources. At some point, the land needed to sustain each person on Earth might exceed the amount of land that is available.

Question (6): This graph shows the world population growth and projected trends in both developed and developing countries.

Developing countries are growing rapidly. The individuals in the pre-reproductive state and reproductive state greatly exceeds those in the post-reproductive state in the population. In developed countries, although the population is increasing, it is doing so at a very slow rate.

LO – 4: Pages: 64, 65, 66, 67,68. [Textbook, figures, 3D] Explain Earth's seasonal cycle and identify solstice and equinox.

Question (1): What effect does Earth's curved surface have on temperatures? Solar energy received at the equator is at a higher concentration. A higher concentration of solar energy means warmer temperatures on Earth.

Solar energy received further away from the equator is at a lower concentration. Lower concentration of solar energy means colder temperatures on Earth.

Seasonal changes do not depend on Earth's distance from the Sun. In fact, Earth is closest to the Sun in January! Instead, it is the tilt of Earth's rotation axis, combined with Earth's motion around the Sun, that causes the seasons to change.

Fall and Winter in the Northern Hemisphere.

Spring and Summer in the Northern Hemisphere

During one half of Earth's orbit, the north end of the rotation axis is away from the Sun. Then, the northern hemisphere receives less solar energy than the southern hemisphere.

During the other half of Earth's orbit, the north end of the rotation axis is toward the Sun. Then, the northern hemisphere receives more energy from the Sun than the southern hemisphere.