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Physics

Why is specific heat important?

Specific heat is defined as the amount of thermal energy required to raise the temperature of a unit mass of a substance by one degree of temperature. It is important because it determines the amount of energy that needs to be added or removed to heat up or cool down a substance or an object. The IB Physics data booklet formula involving specific heat is $\hspace{2em}$ $Q = mc\Delta T$ Where $\hspace{2em}$ $Q$ is the heat required in J\ $\hspace{2em}$ $m$ is the mass of the sample in kg\ $\hspace{2em}$ $c$ is the specific heat capacity of the substance \ $\hspace{2em}$ $\Delta T$ is the change in temperature in k. This formula can be rearranged to solve for specific heat capacity to get $\hspace{2em}$ $c = \dfrac{Q}{m\Delta T}$ We can see from the formula that the units on $c$ will be J kg$^{-1}\ ^o$C$^{-1}$. Substances with high values of specific heat require more energy for a given change in temperature than substances with a lower value for specific heat. Water is an example of a substance with a high specific heat, with $c$ equal to 4186 J kg$^{-1}\ ^o$C$^{-1}$. This relatively high value means that a significant amount of energy is required to raise water to its boiling point. It also means that a lot of energy is released when water cools down again. Some older heating systems in houses circulate hot water to deliver heat to the rooms. Water’s high carrying capacity for thermal energy makes it ideal for this use. Another example of where water’s high specific heat plays an important role is in weather. Although the land may heat up and cool down relatively quickly as the air temperature changes, bodies of water will take much more time for their temperature to change. In summer, the water will stay cooler than the air and help moderate extreme heat. Similarly, in winter bodies of water can help moderate very cold air temperatures. Because of our understanding of specific heat, we can calculate the heat capacity of objects. This is the amount of energy required to raise an object's temperature by one degree kelvin. Once this is known, we can predict the rate at which objects will change temperature and the amount of heat energy involved. Understanding specific heat is extremely valuable for designing systems where heat transfer is fundamental to their operation.

Biology

What does starch do for a plant?

Starch plays a vital role in plants by serving as a storage form of glucose. During photosynthesis, plants often produce more glucose than they immediately require. To manage this surplus, they convert the excess glucose into starch—a carbohydrate that can be hydrolysed and respired to release energy when needed. This stored energy supports essential processes such as growth, repair, and survival, particularly when photosynthesis slows or stops, such as at night or during winter. Biochemically, starch is composed of two types of polysaccharides: amylose and amylopectin. Amylose consists of alpha-glucose units joined by α 1-4 glycosidic bonds, forming a linear, coiled structure. Amylopectin, by contrast, is branched and contains both α 1-4 and α 1-6 glycosidic linkages between the alpha-glucose molecules. The α-1,6 glycosidic linkages cause branching, which allows amylopectin to be broken down more rapidly than amylose. This structural difference makes amylopectin particularly useful when the plant needs to quickly access stored glucose. Starch is typically stored in organs such as roots, seeds, tubers, and some leaves. When environmental conditions limit photosynthesis, the plant hydrolyses starch back into glucose. This glucose is then used in cellular respiration to generate ATP, providing energy for vital metabolic activities. Because starch is insoluble, it does not affect the osmotic potential of the cell where it is stored, allowing glucose to be stored without disrupting water balance. This property allows plants to store large quantities of glucose without disrupting cellular function or water potential. In summary, starch enables plants to maintain a stable and accessible energy reserve. Its biochemical structure, efficient storage capacity, and osmotic neutrality make it ideal for managing energy needs when photosynthetic activity is reduced. This function is fundamental to plant survival, development, and adaptation to changing environmental conditions.

Psychology

What is an MRI in psychology?

Magnetic Resonance Imaging (MRI) is a brain imaging technique that uses strong magnetic fields, radio waves, and a computer to produce detailed 2D or 3D images of brain structure, which can then be analysed by a trained professional. This method allows researchers to explore how differences or changes in brain structure may be linked to changes in behaviour, and vice versa. One strength of MRI is that it is safe and non-invasive, allowing repeated scans to be conducted without exposing participants to harmful radiation. This makes it useful for studying long-term changes in the brain. However, a limitation is that MRI only provides structural information, not data about brain activity. It is also expensive and requires participants to remain very still during the scan, which can be challenging for certain groups and may limit its accessibility in some research contexts. In psychology, researchers use MRI to study how the brain develops from childhood to adulthood, helping them understand typical brain maturation and how it relates to behaviour and cognitive abilities. MRI is also used to show neuroplasticity, revealing how the brain physically changes in response to learning and experience.

Physics

Why does v = fλ?

The universal wave equation v = fλ is one of the fundamental equations in Physics. It relates the speed of a wave, v, the frequency, f, and the wavelength λ. Waves are periodic disturbances that propagate energy through a medium. They are caused by an oscillating source that creates the original disturbance. The frequency of the resulting wave is equal to the frequency of the source. The period $T$ of the oscillation is the inverse of the frequency $f$. One period is the time that it takes for the source to complete a full cycle and return to its original position. The particles in the medium propagate the wave through individual oscillations with this same period. The wavelength $\lambda$ of a wave is defined as the distance between two successive points on a wave that are oscillating in phase. An example of points on a transverse wave that are in phase with each other are crests - at a crest the particles are at the top of their oscillatory motion. Similarly, all points on troughs are in phase with each other. So the distance between adjacent crests or troughs is one wavelength. For a longitudinal wave, a wavelength is the distance between the centers of two adjacent compressions or rarefactions. Now we can think about how far a wave travels in the time that it takes the source disturbance to repeat itself, or in other words, complete one cycle. The time for one cycle is the period $T$. Waves will travel away from the source at a speed $v$. This speed depends on the nature of the medium and is independent of the frequency of the source. If we consider a wave that travels away from the oscillating source, we can use the speed equation $v = \dfrac{s}{t}$ to determine that the distance $s$ that the wave travels in one period $T$ is given by $\hspace{3em} s = vT $ This distance is the separation between two repeating points on the waveform, and so is equal to the wavelength $\lambda$ $\hspace{3em} λ = vT$ Solving for the speed gives $\hspace{3em} v = \dfrac{\lambda}{T}$ And we know that the period is the inverse of the frequency $\hspace{3em}T = \dfrac{1}{f}$ Substituting in, we arrive at the wave equation $\hspace{3em} v = f \lambda$

Chemistry

Why does electronegativity increase across and up the periodic table?

Electronegativity increases across a period (left to right) and up a group because of the combined effects of atomic size and effective nuclear charge. Electronegativity is the ability of an atom to attract the shared pair of electrons in a covalent bond. As you move across a period, the number of protons increases while electrons are being added to the same shell, resulting in a higher effective nuclear charge, which is the net positive charge experienced by valence electrons after accounting for shielding. Since the shielding remains relatively constant across a period (same number of inner shells), the increased nuclear charge pulls the valence electrons more tightly, making the atom smaller and better able to attract bonding electrons. This is why fluorine, at the far right of Period 2, is more electronegative than carbon or nitrogen in the same period. Moving up a group, electronegativity increases primarily due to decreasing atomic size. As you go up a group, there are fewer electron shells between the nucleus and the bonding electrons. For example, fluorine (Period 2) has only two electron shells while iodine (Period 5) has five. When atoms form covalent bonds, the shared electrons in smaller atoms are much closer to the nucleus and experience a stronger electrostatic attraction, despite the smaller number of protons. The effect of decreasing distance outweighs the effect of decreasing nuclear charge as you move up a group. These two trends combine to make fluorine, located in the upper right of the periodic table, the most electronegative element with a value of 4.0, while francium in the lower left would be the least electronegative. The only exception to the trend is the noble gases, which typically don't form bonds and therefore don't have standard electronegativity values.

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