Ratio of KE to GPE at 10m
Category Archives: P1
Which V I readings are for torch lamp?
Pure Physics 2019 P1Q33 and 2007P1Q28
Torch lamp or bulb is a non-ohmic conductor. The V-I graph has an increasing gradient indicating resistance increases. As the current through the filament of bulb increases, temperature increases and resistance increases.
For an ohmic conductor, the graph of V against I is a straight line with constant gradient and passes through the origin.
Something to thing about:
What if there is an option E where
V increases from 0, 1, 2, 3
I increases from 0, 6, 10, 12 respectively
The graph will be a typical ohmic graph, similar shape to option B, but will you choose E?
Refer to the last section of the video from 4:37 s.
Direction of friction on the wheel
There have been a few questions in Olevel asking students the direction of the friction on the wheel, It is important to consider if the wheel is connected to the engine or not.
Below is an illustration on this concept.
You can view the explanation plus the 4 examples from Olevel p1 in the video below.
Examples
Refer to the video above for the answers
2013 PurePhysics P1Q30 – Direction of the electric field
Ans: Option A
View the video tutorial for the explanation:
2021 SciPhy P1Q15 Electric field lines between the two charges
View the video tutorial for the explanation
Determine the motion of the particles on transverse wave
Instead of imaging how the particles will move and guess their motion, there is a technique which can help you to determine that.
In addition, when particles are in phase, it means that both particles on the wave have the same velocity and same displacement. It means both have the same speed in the same direction and same distance and direction away from the rest position.
Particles that are out of phase means both are having the same speed but in opposite direction.
Refer to the video below to find out more.
Question 01: 2005/2008 PP P1 Q20/Q18
Question 02: 2018 PP P1 Q24
Barometer with a layer of water – Find height of mercury H
PP2017p1q21 Sound – time taken for the next rarefaction to arrive at the point P
DC Question – Find unknown R, given the voltmeter readings when switch P and Q are closed respectively
Answer: Option A
Temperature – Thermocouple – Find the unknown temperature
Answer: 800 oC
Determine focal length of lens using mirror with object and image aligned
Click on the link below to view another similar question.
Distance of sound detector from walls
Answer: Option B
Minimum distance h mirror from the floor
Answer: B
Which direction is the Friction of the wheel?
Try these two questions. The phrase ‘the wheel is driven/connected to the engine’ is important actually. Hopefully you will know how to solve them!
Finding specific latent heat of vaporisation (lv) (pure physics)
Take note that the question is looking for specific latent heat of vaporisation during boiling. Hence information of mass m1 before heating is not relevant. There is no change of state of the water, it is merely the heating of the water (which involves specific heat capacity of water).
Refer to the worked solution below.
Solutions: Option D
Pressure – Height of ethanol in the column
Answer: Option D
2016 Pure Physics P1 Q40 – Voltage and Power of Bulb Y when X is switched off
Solutions: Option C
[There is another similar question in 2013 Nov Pure Physics P1Q40. The answer is Option C too. Refer to the last section of this post]
Refer to the 2 videos below. The 1st one is faster if you know that the bigger the resistance, by proportion, the bigger the potential difference of the component as it will take a larger portion of the emf wrt to the other components in series. This method is especially useful for MCQ.
If you are still unsure, you may put in values to find the I, V and P across the components. This will be more tedious and time-consuming.
Another similar question is 2013 Nov Pure Physics P1 Q40.
Solutions: Option C
Another P1V1 = P2V2 question
Solution: Option C
Cells in parallel vs single cell
Answer: Option C
2013 SPP1Q2 Finding resultant force from 2 forces at 0 to 90 degree
Answer: Option A
Refer to the video tutorial for the explanation.
resultant force-time graph link to speed-time graph
Answer: Option A
Refer to the video tutorial below for explanation.
Identifying what lens, focal length and image from 2 rays – PP2010P1Q23 and SP2014P1Q11
These 2 questions are actually the same. Q23 is from 2010 Pure Physics P1 while Q11 is from 2014 Sci Physics P1. Take a look at these 2 questions. If you are not sure, view the video below for the explanation.
Answer to Q23: Option A
Answer to Q11: Option D
If you do not know how to answer these 2 questions, view this video and also refer to the lens summary below.
Which is better to cool the food?
Other examples in our daily lives:
In some supermarket, the seafood are placed outside of air-conditioned place. The seafood is kept cold by putting crushed ice covering the seafood to keep the them cold and fresh.
Refer to this Sci Physics question N2008P2Q6(b)
Solutions:
For the solid that does not melt, when thermal energy is absorbed from the surrounding food, its temperature starts to rise. So it is not so effective at keeping the food cool.
For ice-pack, when thermal energy is absorbed from the surrounding food, it starts to melt. During melting process, a much larger quantity of thermal energy is absorbed from the food to melt per unit mass of ice, the temperature remains constant at 1oC, and the melting process is long. Hence ice-pack is more effective at keeping the food cool.
Related posts about ice:
Density of ice – Why ice floats on water?
Will whole lake be frozen during winter?
Time interval between two sounds from a gun – direct and reflected sound
Solutions: Option B
You can view the video tutorial here or the written solutions below.
Minimum force F to push barrel up a step
Solutions: Option D
You can view the video tutorial here or the written solutions below.
(You can click here to view another post on similar question where angle is given instead)
2013SPp1q17 What is the new P when V across resistor is doubled?
Solutions: C
Alternatively, you may put values to work out using the 2 basic formulae of P = IV and V = IR. Refer the video below.
Wave – Displacement-time graph of a particle on a wave
Solutions: Option C
Consider positive displacement if the particle P is above the undisturbed position, and negative displacement if the particle is below the undisturbed position.
The next instance, the particle P will be moving vertically downwards, i.e. moving nearer to its undisturbed position. So the displacement decreases to zero before it moves below the undisturbed position (negative displacement).
SP N2007 P1 Q16 – Which events will cause the fuse to blow?
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.
What is the speed-time graph of the object when pulling force is removed?
A constant horizontal force F, of magnitude 16 N, is applied to an object at rest on a rough surface. The constant force of friction is 8 N. At X, the force F is removed.
Which speed-time graphs correctly shows the motion of the object?
Solutions: Option B
Either B or D is correctly. But you need to find the magnitude of the deceleration after X in order to determine if the magnitude (gradient) is greater or smaller than the magnitude of the acceleration before X.
Option: A
Ratio of masses of same substance when heated
Two blocks X and Y, which are made of the same metal, are heated by heaters of the same power rating. The variation of temperature with time of both blocks is shown on the same graph below.
What is the ratio of the mass of X to that of Y?
A Â 1 : 3 Â Â Â Â Â B Â 1 : 4 Â Â Â Â C Â 3 : 1 Â Â Â Â D Â 4 : 1
Option: B
Induced emf not affected by resistance of wire
The electromotive force (e.m.f.) induced in a conductor moving at right-angles to a magnetic field does not depend upon
A) the length of the conductor.
B) the resistance of the conductor.
C) the speed of the conductor.
D) the strength of the magnetic field.
Solutions: B
The longer the wire, the rate in which the magnetic lines of force cutting the wire is greater. So A is true.
As it is a wire and not a closed circuit, no induced current is formed. Hence induced emf is produced and the resistance of the wire will not affect the in emf induced.
Object falling at freefall
A particle released from rest at O falls freely under gravity passes through P and Q as shown.
If the particle takes 4 s to move from P to Q where PQ = 120 m, how long does it take to fall from O to P?
A) 1s B) 2s C) 4s D) 8s
Solutions: Option A
Converging Lens – Which ray is correct after passing through the lens
Which of the following light rays behaves correctly when it passes through the converging lens?
Solutions: Option C
Refer to the following diagrams and recall the basic.
From the diagram above, only when parallel beam of light passes through the converging lens and converge to a point, that point is known as focal point, F. Only then, the distance between F and optical centre, C, is known as the focal length, f.From the diagram above, note that when light ray from object is parallel to principal axis, it will pass through F after passing the converging lens.When light ray passes optical centre, it will pass straight. When light ray passes F and then the converging lens, it will be parallel to the principal axis.
A is wrong as it should be parallel to principal axis after passing through the lens.D is wrong as if after the lens the ray is parallel to principal axis, it must pass through F initially before entering the lens.
The 3 rays shown in the previous diagram are not the only rays from object. In fact, light shines on any point on the object, light is reflected in all direction. We usually concentrate on the 3 rays from drawing of image and its properties (as mentioned above).
For the other rays likewise, all reflected light from that particular point on object will be converged to the same particular point on the image.Hence, B is wrong as did not pass through F before hitting the lens, the light will definitely not pass through F on the other side.Only C is correct.Another important concept, when a parallel beam of light strikes the lens, the light rays will converge to a point which falls along the focal place. Refer to diagram below.
Click the following posts for other lens concepts:
N2007P1Q20 Light – Mirror Image through Periscope
The diagram shows an object O viewed using two mirrors. A person looks into the mirrors as shown. At which position is the image of O seen.
Solutions: Option D
To solve this kind of question, you have to do in stages.
1) Consider the object O and the mirror at the top. The image formed will be equal distance perpendicular to the mirror (follows the 5 characteristics of mirror image). Let the image be O’.
2) Now treat O’ as the new object and consider the mirror at the bottom. Likewise apply the same principle, the image of O’ is now at position D. Alternatively, a fast and simple way is based on the concept that to our eyes, light seems to travel in straight line. Hence to our eyes, the image of O is directly in front.
Evan's Space 