Answer: Option D Alpha emission is the least penetrating, easily be blocked by a few cm of air, skin or thin paper. Beta emission can be blocked by a few cm of aluminium. Gamma emission can be blocked by a few cm of lead or metres of concrete. Refer to the video to understand how to apply the concepts.

Answer: Option C With first glance, we may think of using kinematics to solve. It can, but the process will be longer. Refer to the video towards the end. For such questions, it will be much easier to use conservation of energy (COE). Besides the usually equating KE to GPE, we must not forget that we can also equate KE to WD. All are energy.

Answer: Option B Emf is the work done (energy needed) to carry a unit charge (1C) through the whole complete circuit. By definition, it is with respect to a unit charge (1C). In general, it can also mean what is the emf when a certain amount of energy is carry certain amount of charge round the complete circuit. Using V = E/Q, as long as the V is 5V, it is correct. Note that 1C is NOT 1 electrons. The amount of charge on an electron is about 1.6 x 10^-19 C. So there are many electrons in 1 C.

Answer: Option B Wavefront is an imaginary line that joins all identical adjacent points that are in phase. So if you assume the circular wavefront that connects Y is crest, than X will be a trough.

Answer: Option A W = mg, where g is the gravitational field strength. g = W/m, hence g is the gravitational force (pull) acting per unit mass of an object. In addition, in the weight-mass graph, the gradient represents the g. I.e the steeper the line, the higher the g for the planet. Mass is the amount of matter in the body. So for this question, it is important to know that mass remains constant whether it is on planet P or Q.

Characteristics of mirror image: virtual (an image which cannot be formed on a screen) same size as object laterally inverted upright distance between object and mirror is equal to distance between image and mirror One difficulty faced by students in such experiment is how to insert the pins with respect to the image of the object. So do watch the video to learn the techniques, which is applicable for refraction too.

Examples of reflection ray diagrams covered in the video.