physics tys Flashcards
State what is represented by the gradient of a velocity-time graph
Acceleration
State, in terms of forces acting, why the man with jetpack remains in mid air.
The magnitude of the upward force exerted by the jetpack on the man is equal to the magnitude of the downward force due to the weight of the man and the jetpack, hence the resultant force acting on the man is 0N.
Distinguish between mass and weight
The mass of an object is a measure of the amount of matter it contains and is a scalar quantity whereas the weight of an object is the gravitational force acting on it and is a vector quantity.
State what is meant by work done
The work done by a force on an object is the product of the force and the displacement made by the object in the direction of the force.
Describe how thermal energy is transferred by convection.
When the air/ water in the surrounding is heated, it expands and become less dense. The less dense air/ water will rise. Cooler air/water on top, being denser, sinks to replace the less dense portions. This sets up a convection current.
State one component of the electromagnetic spectrum that is an ionising radiation and its uses
Gamma rays. To kill cancer cells during cancer treatment
With a cloth, explain how screen becomes positively- charged.
The cloth pulls electrons from the atoms of the screen causing the screen to become positively-charged
State one advantage of using a circuit breaker rather than a fuse
A circuit breaker can be easily reset and reused whereas a fuse has to be replaced when blown.
State what is meant by the efficiency of a solar cell
The efficiency of a solar cell is the ratio of useful electrical energy output to the total light energy input.
Define the term refractive index in terms of the speed of light
The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium.
Explain why and how light is totally internally reflected
When light travels from an optically denser medium to an optically less dense medium, there exists a critical angle for which the angle of refraction in the optically less dense medium is 90º. When the angle of incidence is greater than the critical angle, the light ray is reflected internally in the denser medium.
Physical quantities, such as resistance of a metal wire, are used to define temperature scale. Explain how this is done for the Celsius scale of temperature.
- Select a lower fixed point ( ice point ) and an upper fixed point ( steam point )
- Take readings of the physical quantity ( such as the resistance of a metal wire) of these fixed points. 3. Label the readings and divide the range of temperature equally between these two fixed points to obtain a scale.
State the reason why the actual energy supplied is greater than the calculated.
Some energy supplied is lost to the surrounding as heat.
State what is meant by the centre of gravity
The centre of gravity of an object is the point where the whole weight of the object appears to act on.
State what is meant by KE and GPE
KE is the energy of a mass due to its velocity
= 1/2 mv^2
GPE is the energy of a mass due to its position in a gravitational field.
Temperature constant, volume of trapped air decreases and its pressure increases. Using ideas about molecules, explain why the pressure increases
The larger number of molecules move at a high speed, colliding against the walls and exerting a force against the wall when they bounce off. The force per unit area exerted by the molecules on the wall is the pressure. When the volume increases due to a higher concentration of molecules in a smaller space, hence a larger pressure
When the resistors are connected in series, what remains constant for the two resistor?
current
When the resistors are connected in parallel , what remains constant for the two resistor?
potential difference
State one other renewable energy source used to generate electrical energy
wind energy
State the relationship between the cross-sectional area of the wire and its resistance
R = pL/A resistance is inversely proportional to cross-sectional area.
3 possible effects on the living cells in the human body when X-rays are absorbed.
- Ionising radiation on cells
- Mutated cells
- Death of cells
Describe the effects on unbalanced forces on the motion of an object
A stationary object will accelerate and move in the direction of the resultant force from the unbalanced force.
A moving object will undergo acceleration in 2 ways, 1. velocity can either increase or decrease. 2. change its direction of motion
Describe what is meant by internal energy
Internal energy refers to the total kinetic and potential energies of the atoms of a body.
State 2 conditions requited for a particles to experience a force in a magnetic field.
- The particle must be charged and moving
2. The changed particle must not be moving in the direction parallel to the magnetic field lines.
State 2 differences between evaporation and boiling
- Evaporation can occur at any temperature where as boiling only occurs at a specific temperature known as the boiling point
- Evaporation happens only at the surface of the liquid whereas boiling happens throughout thee liquid
State one difference other than their speeds, between sound and light
Sound requires a medium to propagate while light can propagate even in vacuum.
State the value of the speed of light in vacuum
3 x 10ˆ8 m/s
Light travels faster in air than in glass, but sound travels faster in glass than in air. Using ideas about molecules, explain why sound travels faster in glass than in air
A medium is required to transmit sound and sound waves vibrate in the medium in the same direction that they travel. Since glass molecules are packed closely together and air molecules are spaced far apart from each other, glass is denser that air and energy from sound waves can be propagated faster between adjacent glass molecules s compared to air molecules. Hence speed of sound is faster in glass than in air.
Define the term focal length of a converging lens
The focal length of a converging lens is the distance between the optical centre of the lens and the principal focus
State the principal of moment
For an object to be in equilibrium, the sum of clockwise moment about a pivot is equal to the sum of anti-clockwise moment about the same pivot.
Define frequency of a wave
Frequency is the number of complete waves produced per unit time.
Describe the motion of the molecules in a liquid
The liquid molecules are packed close to each other in an irregular manner, but not as close as in solids. Hence the liquid molecules can have both vibrational and translational motions and can move around within the bulk of liquid by sliding past one another.
State Ohm’s law
Ohm’s law states that the potential differences across a conductor in a closed circuit is directly proportional to the current flowing through the conductor provided. Other physical conditions of the conductor such as its temperature remain constant.
State what is meant by condensation
Condensation refers to the change of state from gas to liquid
State what is shown by the direction of the electric field
The direction of the electric field indicates the direction of the electric force that will act on a positive charge placed in the field.
State why the filament lamp does not obey Ohm’s law
When the current increases, the filament’s temperature increases and hence its resistance will not remain constant but increase
Define emf
Emf refers to electromotive force and is defined as the work done by a source in moving a unit charge around. a close circuit.
Describe the potential hazards of using electricity from the main socket
- Electrocution hazard : The live terminal from the main socket has very high potential. If the appliances are not insulted/ earthed properly, and there is a fault, any user touching the appliances can be electrocuted.
- Fire hazard ; When too high current is drawn from the mains through the cables of the appliances, the cable insulations can melt and burn. The electrical fire will require a special fire extinguish to extinguish
State 2 reasons why collisions between air molecules and smoke particles cause the smoke particles to move randomly
- Air molecules are in constant random motion : different air molecules are moving at different velocities at any instance.
- Air molecules collide with each other.
When the temperature of air inside a glass box increases, the molecules move faster. Explain why this increases the pressure of the air
An increase in temperature increase the KE of the air molecules. This causes them to move faster and collide more frequently with the smoke particle and the glass box’s walls. The force per unit area exerted by each air molecules on the walls of the box is the pressure exerted by each air molecules. Since the frequency of collisions increases, the pressure exerted by the air also increases.
Explain in words what is meant by the critical angle
Critical angle is the angle of incidence in a denser medium for which the angle of refraction in the less dense medium is 90º
State what is meant by current in an electric current
Current in an electric circuit is the rate of flow of charge in the circuit and it is measured in amperes.
Explain what is meant by pd.
P.d refers to the potential difference across a circuit component which is the work done to drive a unit charge through the circuit component.
