mechanics, materials, electricity

Question 1

Current

Answer 1

• Movement of charge carriers

The greater the Current…
- The more carriers that flow
- The quicker the charge carriers flow

Question 2

What is EMF?

Answer 2

The energy supplied by the power source to each unit of charge (1C)
- 1C = 1As
- EMF = P.D + Lost Volts
- lost volts = energy lost due to resistance.

Question 3

What are lost volts?

Answer 3

Energy dissipated per unit charge

Question 4

What is potential difference?

Answer 4

The energy transferred from the charge to the output of the electrical circuit is the P.D..
/
ability for the charge carriers to do work

Question 5

Kirchoff’s 1st Law

Answer 5

Law 1: charge is conserved in an electrical circuit
- The sum of current into a junction = sum of current out of
a junction
- at a junction current splits in inverse to total resistance of
each path (e.g. see example below)
- Current entering a component is the same as current
leaving a component.
- The current passing through two or more components in series is the same through each.

Question 6

Kirchoff’s 2nd Law

Answer 6

Law 2: energy is conserved in an electrical circuit.
- loop law/closed circuit law
- the algebraic sum of P.D.s in any loop must equal zero
- can find P.D. at component using the Directly Proportional relationship of P.D. and Resistance.
- Potential difference across components in parallel are the same (each loop is considered a closed system)
- For any complete loop of a circuit, the sum of the EMF is equal to the sum of the potential drop around the loop.

Question 7

Principle of Moments

Answer 7

Anti-Clockwise Moments = Clockwise Moments

Question 8

Magnitude of Moments

Answer 8

The moment is dependent on
- the magnitude of the force ( larger force, greater moment)
- perpendicular distance ( greater distance, greater moment)
M=fd
NM = N x m

Question 9

Couples

Answer 9

A couple is a pair of forces acting on a body that are of equal magnitude and opposite direction, acting parallel to one another, but not along the same line

thus the resultant force is zero but the resultant moment is a non-zero value

A couple causes a turning effect but not by accelerating, instead by changing direction.

Question 10

Centre of Mass & Weight

Answer 10

The point at which all the mass of an object is concentrated

The point at which all the weight of an object is concentrated

Question 11

CM —> M
CM^2 —-> M^2
CM^3 —> M^2

Answer 11

%\x1000
%\x 10,000
%\x 1,000,000

Question 12

Hooke’s Law

Answer 12

The force needed to stretch or compress a material is directly proportional to the extension or compression of the material from its natural length provided the limit of proportionality hasn’t need exceeded.

Question 13

What is the UTS?

Answer 13

The ultimate tensile stress of a material is the greatest stress a material can handle.
_ for materials with high UTS’ we consider them to be stronger materials.

Question 14

Brittle

Answer 14

A material that fractures without significant plastic deformation.

Question 15

Ductile

Answer 15

The degree to which a material can withstand plastic deformation without fracturing.

Question 16

Newton’s 1st Law

Answer 16

Object remains at rest or at constant velocity unless a resultant force is enacted upon it.

Question 17

Inertia

Answer 17

• The tendency for an object to resist changes in velocity.
• ## Objects of greater mass have a greater inertia

Question 18

Newton’s 2nd Law

Answer 18

The resultant force is directly proportional to the product of an object’s mass and acceleration

Question 19

Why may an object moving upwards but slowing down experience a force downwards/ feel lighter?

Answer 19

Because an object decelerating is the same as on object accelerating downwards, thus the resultant force is downwards.

Question 20

Newton’s Third law

Answer 20

If object A exerts a force on object B, then object B exerts an equal and opposite force of the same type on object A.
- The action and reaction forces must be the same and equal.

Question 21

How does newton’s third law explain the motion of a vehicle?

Answer 21

The frictional force of the tire on the ground pushes it back whilst the frictional force of the ground on the tire pushes it forwards.

Question 22

Answer 22

Question 23

Conservation of Momentum

Answer 23

the momentum before = momentum after
given a CLOSED SYSTEM with NO external forces

Question 24

Circuits in Parallel

Answer 24

• For components in parallel the potential difference is the same
• The total current in to a junction must equal the total current out of the junction
• Most of the current flows through the route with the smallest resistance.
• adding resistors in parallel decreases TOTAL resistance by providing an additional path for the current to flow through.

Question 25

the definition of potential difference/ voltage

Answer 25

the work done per unit charge across a component

Question 26

Circuits in series

Answer 26

• for components in series the current flowing is the same (current in = current out)
• the potential difference is shared in the same ratio as resistance
• adding resistors in series increases TOTAL resistance and therefore DECREASES current

Question 27

What effect does adding a component to a circuit have if it’s in:
Series
Parallel

Answer 27

SERIES <—
- total resistance will increase because current will have to flow through all components/resistors
- this decreases current flow because V=IR (for a given p.d.)

PARALLEL <—
- total resistance will decrease because the current now has additional paths to flow through
- increases the current that can flow for a given pd

Question 28

Ohm’s Law

Answer 28

The potential difference across a metallic conductor is directly proportional to the current through it, provided the physical conditions do not change.

Question 29

Negative Temperature Coefficient Thermistor

Answer 29

• A thermistor where when the temperature goes up the resistance goes down