• A-Level Physics Notes Syllabus 2015

Available here is a set of A-Level notes for Physics (9702) syllabus. It contains both AS and A2 chapters.

Even students of the later syllabus may use these notes as most of them is still relevant to the new syllabus.


Link: A-Level Physics Notes Syllabus 2015
Credit: Neha of India


The chapters included are:

1. Units and Measurements
2. Deformation of Solids
3. Electric fields
4. Electric current, potential difference and resistance
5. Resistance and resistivity
6. Practical circuits
7. Waves
8. Superposition of waves
9. Stationary waves
10. Forces, vectors and moments
11. Momentum
12. Waves, energy and power
13. Projectiles
14. Radioactivity
15. Accelerated motion
17. Circuit motion
18. Gravitational fields
19. Oscillations
20. Communication systems
21 Thermal physics
22. Ideal gases
23. Coulomb's law
24. Capacitance
25. Electronics
26. Magnetic fields
27. Charged particles
28. Electromagnetic induction
29. Alternating current
30. Quantum physics
31. Nuclear physics
32. Medical imaging


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• Circular motion in a vertical plane

Consider a pail of water whirling at the end of a rope in a vertical circle. The tension T in the rope varies with the position of the pail.

The figure below shows the forces acting on the pail when the rope is at an angle of θ to the vertical.

From Newton’s 2^nd law: Resultant force F = ma

Net force towards the centre of the circle O is

T – mg cosθ

The net force provides the centripetal acceleration.

Therefore, T – mg cosθ = mv² / r

where v = speed of pail; r = radius of circle

Tension T = mv²/r + mg cosθ

Now, let’s consider how the tension changes as the position of the pail changes.

·         When the pail is at the lowest point (θ = 0),

Tension T = mv²/r + mg        (which is the maximum tension)

·         When the rope is horizontal (θ = π/2 (=90°) or θ = 3π/2 (=270°)), cosθ = 0 and thus

Tension T = mv²/r

·         When the pail is at the highest point (θ = π = 180°), cosθ = –1 and

Tension T = mv²/r – mg        (which is the minimum tension)

Now if the pail reaches the highest point (at a distance equal to the radius r form centre O of the circle), the rope must be taut (there should be a tension in the rope, which is not zero).

( T = mv²/r – mg )      > 0

mv²/r > mg

v > √(gr)

Thus, they velocity of the pail at the highest point must be greater than √(gr).

Now consider the forces acting on the water in the pail when it is at the highest point.

For the water not to fall out (that is, the water is in contact with the pail – there is a contact force on the pail), there should be a reaction R (from Newton’s 3^rd law) on the water by the base of the pail. The resultant force towards the centre of the circle is

F = R + mg = mv² / r

The centripetal force is provided by the reaction R and the weight mg.

R = mv²/r – mg

For the water not to fall, R > 0 (that is, there should be a reaction R on the water).

( R = mv²/r – mg )      > 0

mv² / r > mg

Therefore, water in the pail does not fall out because the centripetal force is greater than the weight of the water. (The weight mg of the water is less than the required force mv²/r towards the centre and so the water stays in. The reaction R of the bucket base on the water provides the rest of the force mv²/r.)

Remember that the weight acts vertically downwards (towards the ground). The centripetal force mv²/r acts towards the centre, causing the bucket to move in a circle.

On the other hand, if the pail is whirled slowly, then mg > mv²/r. The weight is greater than the centripetal force and the water falls out of the bucket. (Here, part of the weight provides the force mv²/r. The rest of the weight causes the water to accelerate downward and hence to leave the bucket.)

References:

1. “Pacific Physics A Level,” by POH LIONG YONG, pg 154 – 155 ‘Motion in a vertical circle’

2. “Advanced Level Physics,” by Nelkon & Parker, 7^th edition, pg 63 – 64

Forces | 9702 Physics Summary Notes

• 5. Forces | 9702 Physics Summary Notes

· Force: rate of change of momentum

· Finding resultant (nose to tail):

o By accurate scale drawing

o Using trigonometry

· Forces on masses in gravitational fields: a region of space in which a mass experiences an (attractive) force due to the presence of another mass.

· Forces on charge in electric fields: a region of space where a charge experiences an (attractive or repulsive) force due to the presence of another charge.

· Upthrust: an upward force exerted by a fluid on a submerged or floating object

· Origin of Upthrust:

Pressure on Bottom Surface > Pressure on Top Surface

 Force on Bottom Surface > Force on Top Surface

 Resultant force upwards

· Frictional force: force that arises when two surfaces rub

o Always opposes relative or attempted motion

o Always acts along a surface

o Value varies up to a maximum value

· Viscous forces:

o A force that opposes the motion of an object in a fluid;

o Only exists when there is motion.

o Its magnitude increases with the speed of the object

· Centre of gravity: point through which the entire weight of the object may be considered to act

· Couple: a pair of forces which produce rotation only

· To form a couple:

o Equal in magnitude

o Parallel but in opposite directions

o Separated by a distance

 

· Moment of a Force: product of the force and the perpendicular distance of its line of action to the pivot 

· Torque of a Couple: the product of one of the forces of the couple and the perpendicular distance between the lines of action of the forces.

· Conditions for Equilibrium:

o Resultant force acting on it in any direction equals zero

o Resultant torque about any point is zero.

· Principle of Moments: for a body to be in equilibrium, the sum of all the anticlockwise moments about any point must be equal to the sum of all the clockwise moments about that same point.