Waves multiple choice questions National 5 Physics

this video is part of series of six that's one for each topic that's intended to take the guess work out of answering multiple choice questions if your knowledge of physics can't lead you to the correct answer you might find that it can at least let you narrow down your choices here's the first question from the waves topic then the diagram represents wave traveling from to the wave travels from to in time of 0.5 seconds which Row in the table shows the amplitude wavelength and frequency of this wave so start with amplitude which looking at the diagram can be measured from the central line to the crest that's the highest point in the wave or from the central line to the trough the lowest point in the wave either way the amplitude here will be 2.6 / 2 which is 1.3 so we can rule out options and already next up to calculate wavelength we need to count the number of waves in the diagram that's 1 2 3 four if the length of four waves is 12 then the wavelength must be 12 / 4 which is 3 now we can rule it option to calculate frequency we use the equation is / number of waves divided by the time taken to produce them if we observed point we'd see all four waves passing in time of 0.5 seconds so substituting those values into the equation gives frequency of 8 Hertz so our answer is here's the next question student makes the following statements about different types of electromagnetic waves one light waves are transverse waves two radio waves travel at 340 m/s through air three ultraviolet waves have longer wavelength and infrared waves which of these statements is or are correct so first off light along with all other electromagnetic waves is transverse wave so 0 one is correct sound on the other hand is longitude wave second of all radio waves don't travel at 340 m/s that's the speed of sound in air radial waves like all other electromagnetic waves travel at 3 * 10^ 8 m/s what about the last Point well here's diagram of the electromagnetic spectrum with the radio waves which have the largest wavelength and lowest frequency on the left and gamma rays which have the shortest wavelength and highest frequency on the right looking at the diagram it's clear that infrared waves actually have longer wavelength than ultraviolet waves so the last point is incorrect meaning our answer is make sure that you have method of memorizing the electromagnetic spectrum so that you can answer questions like this one as well as one that will come up later one method is to remember this phrase raging martians invade Venus using x-ray guns although other phrases are available next question ray of red light passes through glass block has shown which Row in the table shows the angle of incidence and the corresponding angle of refraction at point and here's the table which will move over beside the diagram so this Ray here is what we call the incident Ray the light comes out of the ray box and then strikes or is incident on the flat surface of the glass block what we call the glass air boundary the Angles and reflection or refraction questions are always measured between the ray of light and this dotted line known as the normal which is 90° to the surface that means that this is the angle of incidence not the angle marked as 55° since the angle between the flat surface and the normal is 90° the angle of incidence must be 90 minus 55 which is 35° already we can rule out three of the answers and this is the refracted Ray and again to measure the angle of refraction we have to find the angle between it and the normal line so that means this angle here its value will be 90 minus 30 which is 60° that means that the answer is and now it's time for another picture around which of the following diagrams shows the defraction of water waves as they pass between two walls bring on the first Contender so what we're looking for here is for the waves to have the same wavelength after passing through the gap between the walls as they do beforehand the wavelength is just the distance from one wave Crest to the next also the waves should be spread out as they pass through the Gap in this diagram the wavelength isn't changing which is good but the waves aren't spreading out which is bad it's no from me next up the waves appear to be bending here after they pass through the Gap but again they're still not spreading out answer gets the thumbs down too what about at last we've got waves spreading out as they pass through the Gap but this answer still isn't the right one since the wavelength before and after the Gap isn't the same onwards to the next answer wavelength the same before and after the Gap tick waves spreading out as they pass through the Gap tick this one looks good to me so it must be the answer imagine there must be something wrong with answer let's take look this one has the same problem as answer the wavelength before the Gap should be equal to the wavelength after the Gap and that's not the case here looks like the correct answer was now it's time for another defraction question but you'll also need to remember your electromagnetic spectrum from before student makes the following statements about defraction defraction occurs when waves pass from one medium into another two waves with longer wavelength defract more than waves with shorter wav length and three microwaves defract more than radio waves which of these statements is or are correct first of all it looks like that first statement is actually describing refraction rather than defraction so it's not correct correct you'll know that if you've watched my video on waves definitions mind you you'll maybe know that if you haven't watched my video but it's still worth look you might also know that statement two is correct waves with longer wavelength defract more than waves with shorter wavelength see physics isn't all about using equations there are some facts that you'll also need to remember so don't forget those six definitions videos now that we know statement two is correct we can use it to check whether statement three is correct or not but we will need our trusty electromagnetic spectrum diagram we can see that radio waves have longer wavelength than microwaves and we know that longer wavelengths defract most so the last statement must be false all this means that our final answer is in case you still wanted to know the correct definition for defraction to correct statement one it is the bending of waves at gap or obstacle so if this video has helped you to get over some obstacles and fill in some Gap in your physics knowledge then why not drop like all over it and drop subscribe on my channel too till next time keep physicing