Physics (IGCSE) Revision

Sound waves are caused by vibrations. When an object vibrates, it creates a disturbance in the surrounding medium, such as air or water. This disturbance travels in the form of waves, which we perceive as sound. The vibrations cause the particles in the medium to oscillate back and forth, transmitting energy and creating the sound waves. Therefore, it is true that sound waves are caused by vibrations.

Diamond is a covalent network solid composed of carbon atoms bonded together in a tetrahedral lattice structure. Each carbon atom forms four strong covalent bonds with its neighboring atoms, leaving no free electrons to move and conduct electricity. Therefore, diamond is an insulator and does not conduct electricity.

The equation F=ma represents Newton's second law of motion, which states that the force acting on an object is equal to the mass of the object multiplied by its acceleration. This means that the force experienced by an object is directly proportional to both its mass and the rate at which its velocity changes. Therefore, F=ma is the correct equation to calculate force.

Any frequency over the limit of 20,000Hz is called an ultralsound frequency. This statement is true because ultrasonic frequencies are those that are higher than the upper limit of human hearing, which is typically around 20,000Hz. Ultrasonic frequencies are commonly used in various applications such as medical imaging, cleaning, and pest control.

The explanation for the given correct answer is that an onshore breeze is indeed caused by the land warming faster and retaining its heat worse than water. This is because land has a greater heat capacity compared to water. As a result, warm air rises over the land and cool air sinks over the water, creating a convection current that leads to an onshore breeze.

Boyle's Law states that the pressure and volume of a gas are inversely proportional to each other at a constant temperature. The equation p1V1 = p2V2 represents Boyle's Law, where p1 and V1 are the initial pressure and volume, and p2 and V2 are the final pressure and volume. Therefore, the statement "Boyle's Law is symbols: p1V1 = p2V2" is true.

Photocopiers use the principle of electrostatic charges to create copies of documents. This principle involves the use of a photosensitive drum that is charged with static electricity. When a document is placed on the glass surface of the copier, light is shone onto it, causing the areas that reflect light to become positively charged and the areas that do not reflect light to remain negatively charged. These charged areas attract toner particles, which are then transferred onto a piece of paper to create a copy of the original document. Therefore, the statement "Photocopiers use the principle of electrostatic charges" is true.

Passing current through a wire does indeed produce a circular magnetic field, as stated by Ampere's law. This is because the flow of electric current creates a magnetic field that wraps around the wire in a circular pattern. Similarly, when current is passed through a coil, it acts as a magnet due to the magnetic field produced by the flow of current. This phenomenon is utilized in electromagnets, where a coil of wire is wrapped around a core material to enhance the magnetic field strength. Therefore, the statement is true.

Leaving air gaps creates pockets of trapped air, which is a poor conductor of heat. This trapped air acts as an insulator, preventing the transfer of heat through conduction. Therefore, leaving air gaps can indeed make a good insulator.

Commutators are indeed used in motors to change the direction of current flow in the coil every half turn. This is necessary for the motor to generate continuous rotation. By periodically reversing the current direction, the magnetic field produced by the coil also reverses, causing the rotor to rotate in one direction. Therefore, the statement is true.

The principle of moments states that the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that point. This principle is used to analyze the equilibrium of objects under the influence of forces and torques. By considering the moments in opposite directions, the principle helps determine whether an object will remain in balance or rotate.

An electromagnetic relay is a device that uses an electromagnet to control the flow of current in a circuit. When a small current flows through the coil of the relay, it generates a magnetic field that attracts a switch, allowing a larger current to flow through the circuit. This means that a small current can indeed control the switching of an even smaller current, making the statement "An electromagnetic relay can turn a small current on using an even smaller current" true.

The correct answer is "work done / time taken". Power is defined as the amount of work done per unit time. This means that power is the rate at which work is done or the amount of work done in a given amount of time. Therefore, the equation "work done / time taken" accurately represents the concept of power.

Refraction occurs when light enters a medium with a different speed, causing it to change direction. This change in speed is due to the change in the optical density of the medium, which alters the path of the light. When light travels from one medium to another, such as from air to water or from air to glass, the speed of light changes, leading to refraction. The change in angle or curvature of the medium does not directly cause refraction, but rather the change in speed of light is the primary factor.

In a Light Dependent Resistor (LDR), the resistance decreases as the intensity of light increases. Therefore, in the absence of light (dark conditions), the LDR will have a high resistance. This is because the LDR's semiconductor material does not receive any photons to excite its electrons and allow the flow of current, resulting in a high resistance.

Brownian motion refers to the random movement of large visible particles, which is caused by the constant collisions with smaller invisible particles. This phenomenon was first observed by the botanist Robert Brown in 1827 when he noticed the erratic motion of pollen grains suspended in water. The motion is a result of the random thermal energy possessed by the smaller particles, such as molecules or atoms, which causes them to collide with the larger particles and impart momentum to them. This explanation of the correct answer suggests that Brownian motion is the term used to describe this random motion caused by smaller invisible particles.

The statement "Power = Energy / time" is true. Power is defined as the rate at which work is done or energy is transferred or converted. It is calculated by dividing the amount of energy by the time it takes to transfer or convert that energy. Therefore, the equation Power = Energy / time is correct and accurately represents the relationship between power, energy, and time.

The statement "Copper conducts electricity because it is a solid" is false. Copper conducts electricity not because it is a solid, but because it is a good conductor of electricity. The conductivity of a material is determined by its atomic structure and the ability of its electrons to move freely. Copper has a high number of free electrons that can easily move through the material, allowing it to conduct electricity efficiently.

P waves, also known as primary waves, are a type of seismic wave that travels through the Earth's interior. These waves are longitudinal, meaning that they cause particles to move in the same direction as the wave propagation. During an earthquake, P waves are the first to arrive at a seismograph station because they travel faster than S waves, which are transverse waves. Therefore, the statement that P waves arrive before S waves during an earthquake is true.

Newton's third law states that every action has an equal but opposite reaction. This means that for every force exerted on an object, there is an equal and opposite force exerted by the object. This law helps explain the concept of momentum and the interactions between objects. It highlights the interconnectedness of forces in nature and how they always occur in pairs.

The statement "Torque = force x perpendicular distance" is true. Torque is a measure of the force that can cause an object to rotate around an axis. It is calculated by multiplying the force applied to the object by the perpendicular distance from the axis of rotation. This relationship is fundamental in understanding rotational motion and is used in various fields such as physics and engineering.

A barometer and a manometer use mercury only because mercury is a dense liquid that is sensitive to changes in pressure. Both instruments measure pressure, with a barometer measuring atmospheric pressure and a manometer measuring pressure in a closed system. Mercury's high density allows it to accurately reflect changes in pressure, making it an ideal choice for these instruments. Chromium, boiling water, and cold water are not used in barometers or manometers.

Inertia is a fundamental concept in physics that describes the tendency of an object to resist changes in its state of motion unless acted upon by an external force. It is a key principle of Newton's first law of motion, which states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This property depends on the mass of the object; the greater the mass, the greater the inertia

The equation for momentum is defined as the product of an object's mass and its velocity. This equation is derived from Newton's second law of motion, which states that the force acting on an object is equal to its mass multiplied by its acceleration. However, in this case, the question specifically asks for the missing factor in the equation for momentum, and velocity is the correct answer.

Speed is a scalar quantity because it only has magnitude and no direction. It represents the rate at which an object changes its position, regardless of the direction it is moving in. Therefore, it does not have a specific direction associated with it. Additionally, speed is a measure of how fast an object is moving, indicating its magnitude.

The correct answer for the first part of the question is 273K. This is because to convert from degrees Celsius to Kelvin, you need to add 273 to the Celsius temperature. Since the starting temperature is 0 degrees Celsius, adding 273 will give you 273K.

For the second part of the question, the correct answer is 68*C. To convert from Kelvin to degrees Celsius, you need to subtract 273 from the Kelvin temperature. Since the starting temperature is 341K, subtracting 273 will give you 68 degrees Celsius.

The equation H = mL represents the relationship between the latent heat (H), mass (m), and specific latent heat (L) of a substance. This equation is used to calculate the amount of heat required to change a substance from a solid to a liquid state, which is known as the latent heat of fusion. Therefore, the statement "H = mL can be used to calculate the latent heat of fusion" is true.

The refractive index is a measure of how much light slows down when it passes through a medium compared to its speed in a vacuum. It is calculated by dividing the speed of light in a vacuum by the speed of light in the medium. Therefore, the correct answer is "medium."

it is 4200

This statement is false. An offshore breeze occurs when the wind blows from the land towards the water. It is caused by the temperature difference between the land and the water. During the day, the land heats up faster than the water, creating a lower pressure zone over the land. This causes the cooler air from the water to flow towards the land, creating an offshore breeze. Therefore, an offshore breeze relies on the water having a larger heat capacity than the land, not a smaller heat capacity.

The number of coils on the secondary coil of a transformer can be calculated using the formula:

(number of turns on primary coil / primary voltage) * secondary voltage

In this case, the number of turns on the primary coil is given as 240, the primary voltage is 120V, and the secondary voltage is 40V. Plugging these values into the formula, we get:

(240 / 120) * 40 = 2 * 40 = 80

Therefore, the number of coils on the secondary coil is 80 turns.

The wavelength of a wave can be calculated by dividing the speed of the wave by its frequency. In this case, the wave is traveling at 45m/s and has a frequency of 3000Hz. By dividing the speed (45m/s) by the frequency (3000Hz), we get a wavelength of 0.015m. Therefore, the correct answer is 0.015 m.

The first law of motion, also known as the law of inertia, states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an external force. In the case of an object moving in the orbit of Earth, it is constantly acted upon by the gravitational force of the Earth, which keeps it in orbit and maintains its constant velocity. Therefore, the first law of motion correctly describes this situation.

The answer 3 x 10^12 is correct because when converting from gigawatts to watts, you multiply by 10^9. So, 3000 gigawatts is equal to 3000 x 10^9 watts, which simplifies to 3 x 10^12 watts.

The efficiency of a system is determined by the ratio of work done to the energy input. This means that the more work that is accomplished with a given amount of energy, the higher the efficiency. The other options, force x speed, work done / time taken, and power input / power output, are not correct explanations for efficiency.

to connect to the coil, not the magnet

The given correct answer states that the pressure in liquids is given by the equation P = pgh, where P represents pressure, p represents density, g represents acceleration due to gravity, and h represents the height or depth of the liquid. This equation is derived from the principle of hydrostatics, which states that the pressure in a liquid at rest increases with depth. Therefore, the pressure in liquids can be calculated by multiplying the density of the liquid, the acceleration due to gravity, and the height or depth of the liquid.

The equation for work done is given by force multiplied by distance. This means that work done is equal to the product of the force applied on an object and the distance over which the force is applied. This equation quantifies the amount of energy transferred to or from an object as a result of the force exerted on it.

The given equation, acceleration = velocity / time, is incorrect. The correct equation is acceleration = change in velocity / time. This is because acceleration is the rate at which velocity changes over time, not just the velocity divided by time. Therefore, the correct answer is False.

The statement "Charles law in symbols: p1V1/T1=p2V2/T2" is true. Charles's law states that the volume of a gas is directly proportional to its temperature, given that the pressure remains constant. The equation p1V1/T1=p2V2/T2 represents the relationship between the initial and final states of a gas undergoing a change in temperature and volume, while keeping the pressure constant. Therefore, the given statement is correct.

it is E= mc(delta)T

A soft iron core is not used to keep a solenoid intact. Instead, it is used to increase the strength and intensity of the magnetic field produced by the solenoid. The soft iron core enhances the magnetic properties of the solenoid by providing a path of low reluctance for the magnetic flux, resulting in a stronger magnetic field.

Radiation is the transfer of heat energy in the form of waves. This means that heat energy can be transferred through the emission of electromagnetic waves, such as infrared radiation. These waves can travel through empty space and do not require a medium to transfer heat. Radiation is an important mechanism for heat transfer, as it allows heat to be transferred from a hot source to a cooler object without direct contact between them.

A thermistor is a type of resistor that has a resistance that changes with temperature. In the case of a thermistor, it has a low resistance when it is hot, not a high resistance. This is because the resistance of a thermistor decreases as its temperature increases. Therefore, the statement that a thermistor has high resistance when it is hot is incorrect.

The correct answer is "angle of incidence= angle of reflection, incident angle, reflected angle and the normal all lie on the same plane." This is known as the law of reflection, which states that when a ray of light hits a surface and reflects, the angle of incidence (the angle between the incident ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal to the surface). Additionally, the incident angle, reflected angle, and the normal all lie on the same plane. This law is fundamental in understanding how light behaves when it interacts with surfaces.

The statement is false because the geographic North pole and the magnetic north pole are not the same. The geographic North pole is the point where the Earth's axis of rotation intersects the Earth's surface, while the magnetic north pole is the point where the Earth's magnetic field points vertically downwards. These two poles are located at different points on the Earth's surface and can vary in their positions over time.

The given statement is false. Electrical field lines always travel from positive to negative. According to convention, electric field lines represent the direction of the force experienced by a positive test charge. Since positive charges repel each other, the electric field lines originate from positive charges and terminate on negative charges. Therefore, the correct answer is false.

When an object is floating freely, it experiences an upward force called upthrust, which is equal to the weight of the fluid it displaces. This is known as the law of floatation. In order for a material to float, its density must be equal to or less than that of the fluid supporting it. Therefore, the correct answers are: a) weight, as the weight of the fluid displaced is equal to the upthrust, and b) density, as the density of the material must be equal to or less than that of the fluid.

The useful power output of the boat can be calculated by multiplying the force used to push the boat in the water by the boat's velocity. In this case, the force is given as 350N and the velocity is given as 35 km/hr. First, we need to convert the velocity from km/hr to m/s by dividing it by 3.6. So, the velocity becomes 9.72 m/s. Then, we can calculate the useful power output by multiplying the force (350N) by the velocity (9.72 m/s), which gives us 3402W. However, since the answer options are in multiples of 10, the correct answer would be 10500W.