Physical Quantity is a quantity that can be measured and it consists of a numerical magnitude (size) and a unit . (e.g. 5m where 5 is the numerical magnitude and m is the unit) 1) The seven base quantities and their SI units Out of the seven, for O level Physics, you are required to learn the first 5 (length, mass, time, current and temperature) . 2) Some common derived quantities and units You can think of base quantities as the smallest building blocks (like Lego bricks). When you combined any base quantities to ‘build’ into something else, they becomes a derived quantity.The derived quantity is ‘derived’ or ‘gotten from’ when 2 or more quantities are combined together. 3) Prefixes for SI units Prefixes are used to represent very large or small quantities.For example, instead of writing 1000000 m, it will be more convenient to write 1Mm, which means the same thing!

Prefixes are used to simplify the writing of very big or very small numbers. For instance, instead of having to write 12 500 000 m every time, you can simplify it by using the prefix mega (M), hence it can also be written as 12.5 Mm. Similarly, 0.00054 s can be written as 0.54 ms. If you are unsure or confused with the unit conversions, you can refer to the following videos. 1) Prefixes can be used for different physical quantities units. 2) Unit conversion with examples 3) Unit conversion for units of area and volume 4) Unit conversion for units of speed and density

Answer: Option C Focal length f is the distance between the focal point and the centre of the lens (optical centre) . Note that only when parallel rays of light enter a converging lens, the rays will converge to a point. That point is considered to be focal point F (principal focus). The distance between focal point F and the optical centre is the focal length f. Refer to below. As none of the options is similar to the above definition, you have to consider that the rays from a distant (far away) object are considered parallel . Hence the sharp image formed on the screen is considered the forcal point F of the lens and the distance between the image and the optical centre is the focal length f. If it is a close object, the rays entering are not considered parallel. Hence even if the rays converged to a point, that point is NOT focal point F and the distance between this converged point and the optical centre is NOT focal length f.

When gas in piston and heated but pressure remains constant. It is easier to explain in terms of the average force acting on a unit area. 2008PPp1q15 Answer: B 2017PPp1q15 Answer: A In short:  Temperature increases , Kinetic Energy increases , Rate of Collision decreases , Collision force on wall increases (due to higher speed), Average force per unit area remains constant , Pressure constant . As piston is free to move, it will move to the right such that the pressure remains constant (equal to atmospheric pressure outside). As the piston moves to the right, the volume inside the piston increases .  Surface area of piston in which the air molecules collide increases . The rate of collision decreases as the number of molecules remains constant. With higher KE of molecules, the molecules will collide the wall with greater force . Though rate of collision decreases, with each collision having greater impact force, this makes average force per unit area acting on the wall of piston remains the same. Hence pressure remains constant. Misconception : Many think that the rate of collision remains the same, which is wrong . Considering per unit area, if rate of collision remains the same, with the speed of the molecules increases, there will be greater collision force with the wall. This will result in the average force per unit area being higher, hence the pressure would increase.  If the rate of collision increased , with the speed of the molecules increases, there will be greater collision force with the wall. This will result in the average force per unit area being much higher, hence the pressure would increase even more.

When a system is in equilibrium , 2 conditions are met. 1) Principle of Moment (POM): Sum of anticlockwise moment = Sum of clockwise moment 2) Net force = 0N; all forces are balanced: Total downward forces = Total upward forces Whenever a force passed through the pivot point, that force will not create any moment as there is no perpendicular distance from the force to the pivot. Hence this force will not be included in the calculation of moments.

Simply put, electric appliance can be very simple with just a live wire bring in the current and a neutral wire to bring the current out. The appliance can just work like this forever (without the hassle of having earth wire, fuse etc), provided there is no electric fault developed. Both the earth wire and the fuse are safety features to protect the user and the appliance respectively . Take a look at the video below to understand the rationale. Recall these notes given:

An electric cable contains three wires live, neutral and earth. The cable is correctly wired to a plug which contains a 3A fuse. The insulation becomes damaged and bare metal wires show. Five possible events can occur. A person touches the earth wire. A person touches the neutral wire. A person touches the live wire. The live wire touches the neutral wire. The live wire touches the earth wire. How many of these five events cause the fuse in the plug to blow? A   1          B   2         C   3         D   4 Solutions: Option B Consider the five events: A person touches the earth wire –  As the person is at 0V, same as the earth wire, there will be no current flowing through the person. So current through the circuit will not be affected, which is lower than the 3A fuse rating. Fuse will not blow. A person touches the neutral wire.-   As the person is at 0V, same as the neutral wire, there will be no current flowing through the person. So current through the circuit will not be affected, which is lower than the 3A fuse rating. Fuse will not blow. A person touches the live wire. – The live wire is at high potential of 240 V. The person will get an electric shock. But a common misconception is that if a person gets an electric shock, the current flowing through him is very large, which is wrong. In fact, the current is very small, much smaller than the fuse rating. Assuming the average body resistance of the person is 100 000 ohms, and the potential difference in Singapore is 240 V, since I = V/R = 240/100 000 = 0.0024 A, which is lower than 3A fuse rating. Hence the fuse will not blow. The live wire touches the neutral wire. – This will create a short circuit as a large current which exceeds the fuse rating will from the live (240 V) to the neutral wire (0V) as that path has very low resistance. The fuse will blow. The live wire touches the earth wire. –  This will create a short circuit as a large current which exceeds the fuse rating will from the live (240 V) to the earth wire (0V) as that path has very low resistance. The fuse will blow.

Answer: Option D

There are 3 scenarios with slight variations. Calculate the force F needed to pull the block up the inclined plane. View the video below to understand how to solve these types of question.

Though slinky coil is commonly used to demonstrate transverse and longitudinal waves, you must not quote it as an example for either of the waves. Transverse waves are waves in which the direction of the wave is perpendicular to the direction of the vibration of the particles. Examples are light wave, water wave or all the waves in the electromagnetic spectrum (which light is one of the waves. Longitudinal waves are waves in which the direction of the wave is parallel to the direction of the vibration of the particles.  Example is sound wave (inludes ultrasound and infrasound) Transverse Waves (slinky coil) Longitudinal Waves (slinky coil) Transverse Waves Animation Longitudinal Waves Animation

When an object is oscillating or vibrating in a wave motion , the speed of the object varies along the path. In this video, there are 3 examples of vibrating object. 1) Mass vibrating vertically from a spring 2) Pendulum bob oscillating 3) A particle vibrating up and down on a transverse wave In general, when the object is at the extreme ends of the oscillation or vibration , it is momentarily at rest . Hence its KE at these points is minimum or 0 J . And in the middle that is where the object is travelling the fastest , hence the KE is the maximum .