Japan 中学2年 Science
Chapters: 4
1. Field 1 (3): Electric current and its uses
Electric current · Current and magnetic field
- Electric Current, Potential Difference and Electric Circuits – Electric current is the rate of flow of charge, I = Q/t, measured in amperes with an ammeter joined in series. Potential difference is the work done to move a unit charge between two points, V = W/Q, measured in volts with a voltmeter joined in parallel. Charge flows only in a closed circuit.
- Magnetic Effect of Electric Current – A wire carrying electric current makes a magnetic field around itself. The field forms circles around a straight wire, becomes nearly straight at the centre of a loop, and is uniform inside a solenoid, which then acts like a bar magnet.
2. Field 1 (4): Chemical change, atoms and molecules
How substances are made · Chemical change · Chemical change and mass
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
- Chemical Reactions and Balancing Equations – In a chemical reaction atoms are not made or destroyed; they only change partners. So a chemical equation must have the same number of each kind of atom on both sides. We balance it by changing the numbers in front of formulas, never the formulas themselves.
3. Field 2 (3): Structure and function of living things
Living things and cells · Plant structure and function · Animal structure and function
- The Cell: Basic Unit of Life – Every living thing is made of cells. Robert Hooke first saw cells in cork in 1665. Cells are prokaryotic (no true nucleus, like bacteria) or eukaryotic (true nucleus). Plant cells have a cell wall, chloroplasts and a big vacuole; animal cells do not. Each organelle has a job. Water enters and leaves cells by osmosis. Cells make new cells by mitosis (growth) and meiosis (sex cells).
4. Field 2 (4): Weather and its changes
Weather observation · Changes in weather · Japan's weather · Benefits and hazards of weather
- Weather and Climate: From the Atmosphere to the Monsoon – The atmosphere is a blanket of air around the Earth: 78% nitrogen, 21% oxygen and 1% other gases. It has five layers; all weather happens in the lowest, the troposphere. Weather is the state of the air on one day: temperature, pressure, wind, humidity, clouds and rain. Climate is the average weather of 30 years or more. India has four seasons, and the monsoon winds bring most of its rain. Burning fuels adds carbon dioxide, which warms the Earth and brings more floods and heatwaves. Our carbon footprint is how much of this gas our life adds.
- Natural Hazards – A natural hazard is a natural event that can harm people and property, such as an earthquake, volcano, landslide, flood, drought or cyclone. It becomes a disaster when it hits people who are not ready. Geological hazards come from inside the Earth; meteorological (weather) hazards come from the air and water. Risk = hazard × vulnerability ÷ capacity to cope, so warning systems, strong buildings and trained people cut the damage.