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To find the average length of the spring, we simply need to add up all the individual measurements and then divide by the total number of measurements taken. So, we calculate the sum as $14.9 + 14.8 + 14.8 + 14.7$, which gives us a total of $59.2$. Since there are exactly four measurements, we divide $59.2$ by $4$, leaving us with an average of $14.8 \text{ cm}$. Looking closely at this result, we can see it already has exactly three significant figures, so no extra rounding is needed. That makes option A the perfect, straightforward match for our calculation.
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Whenever you are dealing with a velocity-time graph, the key is remembering that the total distance traveled is equal to the area trapped underneath the line. We can easily solve this by splitting the shape into three simple geometric parts: a triangle, a rectangle, and a trapezium. First, the triangle from $0$ to $10$ seconds has an area of $\frac{1}{2} \times 10 \times 10 = 50 \text{ m}$. Next, the middle rectangular section from $10$ to $25$ seconds covers an area of $15 \times 10 = 150 \text{ m}$. Finally, the trapezium from $25$ to $35$ seconds gives us an area of $\frac{1}{2} \times (10 + 20) \times 10 = 150 \text{ m}$. Adding them all together, $50 + 150 + 150$, gives a total distance of $350 \text{ m}$.
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It is very common to mix up mass and weight in everyday conversation, but in physics, they represent two fundamentally different concepts. Mass strictly refers to the actual quantity of matter inside an object, and we measure it using kilograms. Weight, however, is the actual gravitational pull or force that a planet exerts on that mass. Because weight is essentially a force, it absolutely must be measured in newtons (N), not kilograms. Therefore, statements 2 and 4 are the physically accurate descriptions of weight.
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To figure out the density of any substance, you need to know exactly two things: its mass and its volume, since the formula for density is $\rho = \frac{m}{V}$. To find the mass of a liquid, you would use the digital balance (typically by weighing an empty container, then the container with the liquid, and finding the difference). Next, to accurately measure the volume of that liquid, you would pour it into the measuring cylinder. A ruler measures length and a stop-watch measures time, neither of which helps us directly find the mass or volume of a liquid.
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Think about how leverage works in real life. Tightening a nut requires a certain amount of “turning effect,” which physicists call the moment of a force. The moment is calculated by multiplying the force applied by the perpendicular distance from the pivot (the nut itself). Since the required moment to tighten the nut stays the same, if you want to apply a smaller force, you must increase the distance from the pivot. Using a spanner with a longer handle gives you that extra distance, making the job much easier on your hands.
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According to Newton’s First Law, an object will only have a zero resultant force acting on it if it is entirely at rest or moving at a perfectly constant speed in a straight line. The ball in option A is moving at a constant speed, the ball in option B is completely at rest, and the floating ball in option D has its weight perfectly balanced by the water’s upthrust. However, the free-falling ball in option C has just been released, meaning gravity is pulling it downwards without any upward force fully balancing it yet. Since it’s accelerating downwards, it definitely has a non-zero resultant force acting on it.
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The stability of any vehicle relies heavily on where its centre of mass is located. An object becomes more stable when its centre of mass is kept as low to the ground as possible. When passengers stand up, particularly on the upper floor of a double-decker bus, they physically shift the overall centre of mass of the bus higher up. A higher centre of mass means the bus is far more likely to tip over if it turns a corner sharply or tilts, hence making it dangerously less stable.
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As an object falls downwards, it is losing height. Since gravitational potential energy depends directly on how high something is, its potential energy must decrease. However, as it falls, gravity causes it to accelerate and move faster and faster towards the ground. Because kinetic energy is the energy of motion and relies on speed, its kinetic energy naturally increases as it speeds up. This is a classic example of energy transferring from a gravitational potential store into a kinetic store.
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In physics, doing “work” simply means that you are transferring energy from one place or form to another. Because work done is completely equivalent to energy transferred, it is measured using the exact same standard scientific unit as energy. That unit is the joule, which is represented by the capital letter $\text{J}$. Just to clarify the others: $\text{N}$ is for force, $\text{N/kg}$ is for gravitational field strength, and $\text{W}$ (watts) is for power.
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The mathematical equation for calculating work done is beautifully simple: Work $= \text{Force} \times \text{Distance moved in the direction of the force}$ ($W = F \times d$). If you want to end up with a larger amount of work done, you need to either push with a stronger force or push the object over a longer distance. If both the magnitude of the force increases and the distance moved increases at the same time, the total work done will definitely increase by a significant amount.
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A mercury barometer works by balancing the weight of the mercury column inside the tube against the atmospheric pressure pushing down on the dish outside. When atmospheric pressure gets stronger, it pushes down harder on the liquid in the dish, forcing mercury further up the glass tube. This means that the height of the mercury column (B) will get longer. Because the total length of the glass tube itself obviously doesn’t change, as the mercury rises, the empty vacuum space at the very top (labelled C) has to shrink and become smaller.
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According to Boyle’s law (or simple kinetic theory), if you keep the temperature steady and squish a gas into a smaller volume, the gas particles will hit the container walls much more frequently. This increased rate of collisions means the pressure goes up over time. Before the squeezing even started, the gas already had a certain initial pressure (it wasn’t starting from a complete zero vacuum), so the graph cannot possibly start at the $(0,0)$ origin. It must start at some positive pressure value on the y-axis and then steadily climb upwards as time goes on, which is exactly what graph C shows.
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Evaporation is a surface phenomenon where molecules in a liquid transition into a gas phase. Inside any liquid, the molecules are moving around at different speeds. Only the fastest-moving molecules—those with the absolute highest kinetic energy—have enough power to break free from the attractive forces holding the liquid together. Since these highly energetic molecules are the ones escaping into the air, the liquid is specifically losing its “more energetic molecules.” This is also exactly why the remaining liquid cools down afterward.
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When scientists construct the standard Celsius temperature scale, they base it entirely on two very specific, universally reproducible physical events involving pure water at standard atmospheric pressure. The “lower fixed point” is universally defined as the exact melting point of pure ice, which is $0^{\circ}\text{C}$. The “upper fixed point” is strictly defined as the boiling point of pure water, which is $100^{\circ}\text{C}$. The highest and lowest numbers visually painted on the glass casing of the thermometer are simply its physical measuring range, not the fundamental scientific fixed points.
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The term “melting point” obviously refers to the exact temperature at which a solid melts into a liquid (statement 2). However, in physics, phase changes are reversible at that specific temperature threshold. For any pure substance, the temperature at which it melts (solid to liquid) is numerically identical to the temperature at which it freezes (liquid to solid). Because melting point and freezing point refer to the exact same temperature value on the thermometer, both statements 1 and 2 accurately describe processes that occur precisely at the melting point.
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An electric fire’s primary job is to keep a room warm by emitting heat, and it does this specifically by throwing out thermal radiation. In physics, thermal radiation is classified as infrared radiation, which is an integral part of the electromagnetic spectrum. On the other hand, generators, motors, and electromagnets are designed to utilize or generate electric currents and simple magnetic fields, not to purposefully broadcast travelling electromagnetic waves (like light or infrared) as their primary function.
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The vast, empty space separating the Sun and the Earth is a vacuum, meaning it contains practically no atoms or particles. Both conduction and convection absolutely require a physical medium (like a solid, liquid, or gas) to transfer heat energy, so they simply cannot work in outer space. Thermal radiation, however, travels via electromagnetic waves (like infrared and visible light), which do not need any medium to travel through at all. Therefore, radiation is the only possible way the Sun’s energy can reach us.
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Refraction is the scientific term for the bending of a wave as it crosses a boundary between two different materials. This bending only happens because the wave is forced to change its travelling speed when it enters the new medium (for example, light slowing down as it enters glass from air). Crucially, the frequency of a wave is determined by its original source and never changes when crossing a boundary, so option C is incorrect. The defining requirement for refraction to occur is a change in the wave’s speed.
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When white light hits a prism, it disperses into the famous rainbow sequence because different colors bend (refract) by different amounts. Violet light slows down the most and bends the sharpest, while red light bends the least. The standard mnemonic for remembering the correct sequential order of the visible spectrum is ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet). If we read the options from bottom to top (violet up to red), option C perfectly matches the correct sequence of violet, blue, green, yellow, orange, and red.
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One of the fundamental rules of reflection in a flat, plane mirror is that the virtual image it creates always appears to be the exact same distance behind the mirror as the actual object is physically sitting in front of it. The image must also sit on a line that is perfectly perpendicular (at $90$ degrees) to the mirror’s surface drawn from the object. Looking at the diagram, point B is the only position that is located straight across from the object and appears equidistant behind the reflective line.
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When drawing ray diagrams for a converging lens, any ray that arrives travelling parallel to the principal axis will be bent so that it passes directly through a very specific point on the other side. This point is known as the principal focus (point S in the diagram). The optical center of the lens sits right in the middle (point R). In physics terminology, the physical distance between the optical center (R) and the principal focus (S) is defined exactly as the focal length of the lens.
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The electromagnetic spectrum is organized by frequency. M has a much lower frequency ($10^6 \text{ Hz}$) than visible light ($10^{14} \text{ Hz}$). The regions of the spectrum with frequencies lower than visible light are infrared, microwaves, and radio waves. $10^6 \text{ Hz}$ represents the lowest end, firmly sitting in the radio wave category. Conversely, N has a slightly higher frequency ($10^{15} \text{ Hz}$) than visible light. The waves positioned just above visible light in frequency are ultraviolet (UV) waves, making B the correct categorization.
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Electromagnetic waves (like microwaves, radio, and ultraviolet) consist of oscillating electric and magnetic fields, are purely transverse, and can easily travel through the complete vacuum of space. Sound, however, is a completely different physical phenomenon. It is a mechanical, longitudinal wave that relies entirely on compressing and stretching physical particles in a medium (like air, water, or a solid block). Without a physical substance to travel through, sound simply cannot exist.
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Light travels incredibly fast, at $300,000,000 \text{ m/s}$, so over a short distance of $100 \text{ m}$, the light from the smoke puff reaches the judge’s eyes almost instantaneously (in a tiny fraction of a microsecond). However, sound is much more sluggish, travelling through air at roughly $330 \text{ m/s}$. To cover that same $100 \text{ m}$ distance, the sound wave takes time: $t = d/v = 100 / 330$, which calculates to approximately $0.3$ seconds. That’s why you always see the visual event before you hear the noise!
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In solid metallic conductors like copper, the atoms themselves form a rigid lattice structure and cannot move around; they just vibrate in place. So, atoms or massive ions don’t flow to carry the current. Instead, metals have a “sea” of freely moving outer-shell particles called free electrons. When a voltage is applied across the wire, it is these tiny, negatively charged electrons that drift through the metallic lattice to create what we call an electric current.
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The resistance of any wire is directly proportional to its length. So, when the student doubles the length of the resistance wire from $50 \text{ cm}$ to $100 \text{ cm}$, the resistance of the wire increases (it actually doubles). According to Ohm’s law ($I = V/R$), if the voltage of the power supply remains constant but the resistance of the circuit goes up, it becomes harder for the electricity to flow. Therefore, the resulting current in the circuit will decrease.
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In electrical physics, the abbreviation e.m.f. officially stands for “electromotive force”. While the historical name contains the word “force,” it is important to remember that it is not actually a physical force measured in newtons. Instead, e.m.f. is a measure of the electrical work done by a power supply (like a battery or generator) per unit of charge flowing around the circuit, and it is measured in volts.
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Static electricity on solid objects is generated entirely through the movement of tiny, negatively charged electrons; heavy protons stay firmly locked tight inside the nuclei of the atoms and cannot jump between objects during rubbing. If the plastic rod ends up with a positive charge, it means it must have lost some of its negative electrons. The friction caused those electrons to be scraped away and physically move from the plastic rod onto the woollen cloth.
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To measure resistance ($R = V/I$), you need to find both the potential difference across the component and the current flowing completely through it. Voltmeters are always wired in parallel across the component they are measuring, meaning meter 1 must be the voltmeter. Ammeters measure the flow of current and are always wired in series directly in the path of the circuit, meaning meter 2 must be the ammeter.
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The standard thermistor used in these circuits is an NTC (Negative Temperature Coefficient) thermistor, which means its resistance behaves opposite to temperature: when it gets hot, its resistance goes down. In a series potential divider circuit, the supply voltage is shared out among the components based directly on their resistance. Because the thermistor’s resistance decreases relative to the fixed resistor, it claims a smaller ‘share’ of the total voltage. Therefore, the reading on the voltmeter connected across it must decrease.
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To make the lamp shine its absolute brightest, you need the maximum possible current flowing through it. According to Ohm’s law, for a fixed voltage supply, maximizing current means minimizing the total resistance of the series circuit. An LDR has its lowest resistance when bright light shines on it. A standard NTC thermistor has its lowest resistance when its temperature is very high. Therefore, combining bright light and a high temperature creates the lowest overall resistance, granting the lamp the most current.
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Because there is only one continuous path for the electricity to flow out of the cell, through the components, and back again with no junctions or branches, this is fundamentally defined as a series circuit. One of the core rules of any series circuit is that the electric current is identical at every single point along the loop. Therefore, if ammeter 2 reads $0.20 \text{ A}$, ammeter 1 must also read exactly $0.20 \text{ A}$.
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A fuse is a deliberate safety device built with a very thin piece of wire designed to protect electrical appliances and household wiring. Its sole job is to monitor the amount of electric current flowing through it. If a fault occurs (like a short circuit) and the current surges to a level that is too large and potentially dangerous, the heat generated inside that thin wire causes it to melt and snap. This breaks the circuit completely and instantly stops the dangerous current.
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When a steady current runs through a solenoid, it generates a magnetic field that is practically identical to that of a classic bar magnet. The magnetic field lines form continuous, closed loops: they emerge from the North pole end, curve around the outside, and re-enter at the South pole end. Compass needles always align themselves perfectly along these magnetic field lines. Option D is the only diagram that correctly shows this continuous looping pattern around the outside of the coil from one pole back to the other.
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A transformer operates by constantly reversing a magnetic field thousands of times a second to induce voltages. Because of this, its core absolutely must be made of a magnetic material that is easily and rapidly magnetized and demagnetized without wasting energy. Soft iron possesses this exact property, making it the perfect temporary magnet. Steel, conversely, is a “hard” magnetic material that stubbornly retains its magnetism, which would severely ruin a transformer’s efficiency.
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A relay functions using an electromagnet to physically pull a switch closed. The core inside the coil (part N) must be an electromagnet that immediately loses its magnetism when the control current is switched off, so it must be made of soft iron. The hinged armature (part P) that gets pulled towards the electromagnet must also immediately release when the power drops; if it were made of steel, it might become permanently magnetized and stick to the core, failing to break the circuit.
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In standard scientific nuclide notation (${}^A_Z X$), the bottom number ($Z$) represents the proton number (atomic number), which is the number of protons. Here, $Z = 27$. The top number ($A$) represents the nucleon number (mass number), which is the combined total number of both protons and neutrons in the nucleus. By adding them together ($27 \text{ protons} + 32 \text{ neutrons}$), we get a mass number of $59$. Therefore, the correct notation is ${}^{59}_{27}\text{Co}$.
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During alpha ($\alpha$) decay, an unstable nucleus of element X ejects an alpha particle (which consists of two protons and two neutrons). Because it loses protons, it fundamentally transforms into a completely new element, Y. However, because it just violently lost positive charge from its nucleus without losing any of its orbiting electrons, the resulting atom Y initially has an imbalance of charge, making it an ion. Thus, atoms of X transmutate into ions of the new element Y.
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Normally, the air gap between the highly charged grid and the wire acts as a perfect electrical insulator, preventing any current from jumping across. However, when alpha ($\alpha$) particles pass through that air gap, their relatively large mass and $+2$ charge violently strip electrons off the surrounding air molecules. This strong ionising effect creates a temporary path of charged ions and free electrons in the air, allowing the high voltage to suddenly discharge and jump across as a visible spark.
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The half-life of a radioactive substance is the precise amount of time it takes for its emission rate (or activity) to drop to exactly half of its current value. Starting at $120 \text{ counts/s}$, after one half-life ($6 \text{ hours}$), the rate halves to $60 \text{ counts/s}$. After a second half-life (another $6 \text{ hours}$), the rate halves again from $60$ down to $30 \text{ counts/s}$. Because it took exactly two half-lives to reach the target rate, the total elapsed time is $2 \times 6 \text{ hours}$, which equals $12 \text{ hours}$.