Basic 1
If you go to the Moon, your weight will be lesser or higher? Explain.
Your weight will be lesser.
Moon has a weaker gravity.
Ignore air resistance.
From the Earth.
Earth has a stronger gravity.
What is the importance of electrons flow in a circuit?
It allows electrical energy to be converted.
A sound is sent from the ship to the bottom of the sea.
The distance between the bottom of the sea and the ship is 750 m.
The sound takes 0.1 second to go to the bottom of the sea and returns to the ship.
Calculate the speed of the sound in the water.
15 000 m/s.
(a) Why must ammeter be connected in series?
(b) Will ammeter not work in any parallel circuits?
(a) It is because current only flows in one pathway in a series circuit.
(b) No. It depends on how you connect the ammeter in the parallel circuit.
What is an open circuit?
Give an example of an open circuit.
It is a circuit where current cannot flow.
Examples include open switch, broken lamp.
Name two actions that will increase the ammeter reading.
(a) reduce the number of bulbs.
(b) increase the number of batteries.
Metals and non-metals both have electrons.
Why are metals conductors but non-metals insulators?
Explain how wearing a cardigan or a sweater can keep them warm.
It traps the air in between the cardigan or the sweater and our bodies.
Do you think all objects fall faster on the Moon or on the Earth? Explain.
Do you think objects of different mass fall at the same rate or different on the Earth and on the Moon? Explain.
Objects fall faster on the Earth because Earth has a stronger gravity.
Almost all objects fall at the same rate to the Moon because there is no atmosphere on the Moon.
Why is there no resistance when Jupiter revolves around the Sun?
Ask your teacher to show you the two different solar eclipses that someone observes.
Explain why there is a difference.
When the Moon is nearer to the Earth, the Moon LOOKS bigger. So, a bigger portion of the Sun gets blocked.
A student measures the surface temperature of the Earth during solar eclipse.
Get the result from your teacher.
(a) Suggest an anomaly in the result.
(b) Do you think how long the solar eclipse occurs.
(a) The temperature at the 4th minute.
(b) 7 minutes.
Jupiter has four Moons.
(a) Draw the positions of the Moons that will give the strongest tidal force.
(b) A moon is at the left of the Jupiter while another is on the right of the Jupiter.
The force acting on the Jupiter partly cancels.
Explain.
(a) correct positions
(b) The Moons may have different masses which have different strength of gravity acting on Jupiter.
So, they can only partly cancel the force from each other.
A slanted ramp is set up.
A toy car is released from the higher end.
(a) What will happen to the toy car.
(b) Explain why the speed of the toy car increases as it moves down?
(c) Suggest one way to increase the speed of the toy car when falling down.
(d) Why does the car finally stop moving?
(a) The toy car will move down.
(b) G.P.E is converted into K.E.
(c) Increase the height of the toy car where it is released.
(d) Due to friction or air resistance, the K.E. is converted into thermal energy and sound energy.
State one similarity and two difference between crust and mantle.
Similarity = both are made from rocks.
Difference = crust is made of solid rocks while mantle is made of molten rocks.
Difference = crust is thinner and colder while mantle is thicker and hotter.
What are the compositions of the air?
Is air a mixture or a compound?
Do you think the composition of the air can change?
Air has about 21% of oxygen, 78% of nitrogen, and about 0.04% of carbon dioxide.
Air is a mixture.
The composition of air can change. For example, carbon dioxide increases in concentration that causes global warming.
Earth has an atmosphere.
Explain why Earth has an atmosphere.
Based on your answer, explain how a rocket can leave the Earth.
(a) Earth has a gravity that can attract those gas particles and keep them on Earth.
However, when something moves at a speed high enough, it can overcome the gravity from the Earth.
That speed is known as escape speed, which is about 11200 m / s.
A parachutist opens a parachute when jumping down from the plane in the sky.
(a) What are the two forces acting on the parachutist when jumping down from the plane.
(b) Explain why it accelerates down to the Earth initially.
(c) Explain why its acceleration decreases when the parachutist is falling after a few minutes.
(a) air resistance and gravity
(b) air resistance is weaker compared to the gravity.
(c) air resistance increases as the speed of the parachutist increases.
Name two disadvantages of connecting components in a series circuit.
1. If one component is broken, the whole series circuit won't work anymore.
2. Adding more bulbs will decrease the current; other bulbs will receive lesser current = dimmer.
The Moon literally has no atmosphere.
Explain why.
The gravity of the Moon is too weak to hold gases to form atmosphere.
A comet may come close to a planet at a high speed.
Explain why coming close to a planet can cause the comet to break into smaller rocks.
As the comet comes close to the planet, the planet’s gravity pulls more strongly on the near side of the comet than the far side.
This creates a tidal force that stretches the comet.
If the tidal force is large enough, it breaks the comet into smaller rocks.
A powered motor is connected to a metal container.
The metal container is lowered down into a well to get some water through a roller.
The input power supplied to the motor is 120 W.
The motor has an efficiency of 70%.
(a) Calculate the useful power output.
(b) State two ways where energy is lost when the metal container is being lowered down into the well.
(c) State one way how the energy can be lost when raising the metal container from the bottom of the well.
(a) 84W
(b)
- sound energy can be produced.
- thermal energy is produced through friction.
(c) overcoming gravity / air resistance.
Lead metal has 82 electrons in an atom.
Copper metal has 29 electrons in an atom.
So, is it appropriate to conclude that lead metal conducts electricity better than copper metal because lead metal has more electrons?
Is it also correct to conclude that all non-metal solids cannot conduct electricity?
No.
Other than having more electrons, it also depends on how easily the electrons can move through the metal.
Lead has the most number of electrons so it is more difficult for electrons to move throughout the metal.
Copper has the least number of electrons so it is easier for electrons to move throughout the metal. So, copper is still a better conductor of electricity.
Graphite can conduct electricity but it is a non-metal. It has free electrons.
In a socket, there are three types of wire.
Live wire = carries current into the electrical applicances.
Neutral wire = provide a path for the current to flow back to the source.
Earth wire = safety wire.
(a) What does it mean by safety wire?
(b) A metal kettle may need an Earth wire but a plastic kettle does not. Why?
(a) Earth wire provides a low resistance pathway for current to flow to the Earth. Instead of flowing through the humans' bodies, the current flows through the Earth wire.
(b) Metal can conduct electricity. If live wire touches the wall of the metal container, it poses risk that the users will get electrocuted. So, an Earth wire is needed to direct the current on the container to the Earth.
When the container is made of plastic, it is an insulator. So, it may not need an Earth wire.