(amendments needed. To be updated soon.)
Category: Combined Physics
Describe the effect of temperature increase on the resistance of a metallic conductor.
The resistance increases as the temperature of a metallic conductor increases, so the resistance is directly proportional to the temperature.
When temperature increases, the amplitude of vibration of atoms increases. As a result, the number of collisions among the electrons and atoms increases, increasing the resistance to the flow of charges through the conductor.
Describe what is meant by “wave motion”.
A wave motion is a movement or a disturbance through a medium, where the individual particles in the medium only vibrate vertically, horizontally, or in a cyclical pattern.
The wave motion can be illustrated:
– In a rope, when one end of a rope is moved in an up-and-down motion in a cyclical pattern.
– In a spring, when the spring is moved in an up-and-down motion, or a back-and-forth motion, in a cyclical pattern.
– In a ripple tank, when the dipper is moved in an up-and-down motion on the water surface, producing water waves.
Movement of electrons in discharge ball
An electrostatic generator is used to produce sparks as shown below.
The belt carries negative charges to the dome, making it negatively charged. Before a spark is produced, the discharge ball becomes positively charged.
Describe and explain the movement of electrons in the discharge ball and in the conducting rod as the ball becomes charged.
The electrons in the discharge ball and in the conducting rod moves downwards through the conducting wire, and to the ground.
Electrostatic charging by induction occurs in the ball and rod as they are placed near to the negatively charged dome. Like charges repel, causing the negatively charged electrons in the ball and rod to move away from the dome, escaping through the conducting wire to the ground.
Movement of air particles in sound waves
A sound wave in air is illustrated below.
Points A, B, C and D are all the centers of regions of compression in the sound wave.
Describe what happens as one complete sound wave moves past a point.
The particles in the air are disturbed by the sound waves and vibrates to and fro, in a direction parallel to the direction of the sound waves.
An air particle in the sound wave will vibrate from its rest position to the left, until it reaches its maximum displacement to the left, then vibrate towards the right, move past its rest position, until it reaches its maximum displacement to the right. Then it vibrates to the left, until it returns back to its original rest position to complete one wave motion of the sound wave.
Differences between boiling and evaporation
| Boiling | Evaporation |
| Occurs at a fixed temperature | Occurs at any temperature below boiling point |
| Quick process | Slow process |
| Takes place throughout the liquid | Takes place at the surface of the liquid |
| Bubbles form | No bubbles |
| Temperature remains constant | Temperature may vary |
| Thermal energy supplied by energy source | Thermal energy supplied by surroundings |
What is “inertia”?
Inertia refers to the reluctance of the object to change its state of rest or motion.
The bigger the mass of a body, the greater its inertia.
(ie, the bigger the mass, the more difficult it is to make a stationary object move, or to make a moving object change its speed or direction, due to its inertia)
State the Principle of the Conservation of Energy
The Principle of the Conservation of Energy states that energy cannot be destroyed or created.
It can only be converted from one form to another, or transferred from one body to another.
The total energy in the system remains constant.
Describe an experiment to determine the centre of gravity of an irregularly shaped thin plastic sheet.
a) Drill 3 small holes on the sheet, as near to the edge as possible, as far away from one another as possible.
b) Hang a plumb line from one of the holes.
c) When the sheet is stationary, trace the vertical line made by the plumb line using a marker.
d) Hang the plumb line from each of the other two holes and repeat the tracing of the lines.
e) The intersection point of the 3 traced lines is the centre of gravity of the plastic sheet.
State Newton’s Laws of Motion
Newton’s First Law of Motion (or Law of Inertia):
Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state.
Newton’s Second Law of Motion:
When a resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force. The product of the mass and acceleration of the object is equal to the resultant force.
Newton’s Third Law of Motion:
For every action, there is an equal and opposite reaction, and these forces act on mutually opposite bodies.