Week 8 and 9 – SS1 Third Term Physics Notes

  WEEK 8
TOPIC: CAPILIARITY
CONTENT: Definition of Capillarity
     Cohesion and adhesion
     Application of capillarity

 Capillarity is defined as the tendency of liquids to rise or fall in narrow capillary tubes.
Cohesive force is the force of attraction between molecules of the same substance
Adhesive force is the force of attraction between molecules of different substance or it refers to the force which makes molecules of different substance to attract.
Application of Capillarity
Adhesion of water to glass is stronger than the cohesion of water, hence, when water is spilled on a clean glass surface, it wets the glass. The cohesion of mercury is greater than its adhesion to glass, hence, mercury spilled 0n glass forms small spherical droplets.
EVALUATION

1. Differentiate between cohesion and adhesion
2. Explain the rise of water in a glass capillary tube using kinetic theory
   

Reading Assignment : Read more on capillarity – New school physics (pg104-105)

WEEKEND ASSIGNMENT
1 Differentiate between cohesion and adhesion
2.Explain the rise of water in a glass capillary tube using kinetic theory

 
WEEK 9
TOPIC: ELASTICITY
CONTENT : Definition of elasticity
     Hook’s law
     Tensile stress, tensile strain and young modulus
Elasticity is the tendency of a material to regain its original size or shape after deformation or after it has been compressed or extended.

 Hook’s law states that provided the elastic limit is not exceeded, the extension in an elastic material (wire) is proportional to the force applied i.e Fαe
F = Ke…………………………………………1
Where K is force constant, stiffness or elastic constant
Force constant is the amount of force that causes a unit extension. It is the ratio of force to extension of an elastic material.
K → force constant, stiffness or elastic constant

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 A →proportional limit
L →elastic limit
B →yield point
OL → elastic deform
BC→plastic deform
Hook’s law applies up to the elastic limit. For load beyond L
the wire (material) stretch permanently. The point where small ↑ in load produces large extension is known as yield point.
Breaking point is the point where the wire cannot withstand any further increase in load.
Yield point : it is the minimum stress/load acting on an elastic material beyond which plastic deformation sets in.
Elastic limit is the maximum load (force) which a body can experience and still regain its original size.
EVALUATION
1. Define (a) elastic limit (b) elastic constant (c) yield point (d) breaking point
2. State Hooke;s law of elasticity
Tensile stress is the force acting on a unit CSA of a wire/rod or force per unit CSA of a wire or rod.
Tensile stress = Force/Area …………………….2
Tensile strain is the extension per unit length
Tensile strain = extension/Original length ……………………..3
Young modulus can be defined as the ratio of tensile stress to tensile strain
Young modules = tensile stress/ tensile strain…………………..4
EVALUATION
1.Define young modulus of elasticity
2. A spiral spring extends from a length of 10.01cm to 10.10cm when a force of 20N is applied on it.Calculate the force constant of the spring
Reading Assignment : Read more on elasticity – New school physics (pg 93-96)

WEEKEND ASSIGNMENT
1.The SI unit of tensile stress is ….. (a) N/m (b) Nm (c) N/m² (d) m²
2.The SI unit of tensile strain is ….. (a) N/m (b) Nm (c) N/m² (d) none of the above
3. The SI unit of tensile strain is ….. (a) N/m (b) Nm (c) N/m² (d) none of the above
4. The SI unit of force constant, K is ….. (a) N/m (b) Nm (c) N/m² (d) m
5. Hooke’s law states that (a) F α A (b)F α e (c) E α F (d) E α A

THEORY

1. A wire is gradually stretched by loading it until it snaps (a) sketch a load- extension graph for the wire
2. indicate on the graph the elastic limit(E), yield point (Y) and breaking point (B)