The electromotive force (emf) of a cell is its terminal voltage when no current is flowing through it. The terminal voltage of a cell is the potential difference between its electrodes. A voltmeter cannot be used to measure the emf of a cell because a voltmeter draws some current from the cell. To measure a cell’s emf a potentiometer is used since in a potentiometer measurement no current is flowing. It employs a null method of measuring potential difference, so that when a balance is reached and the reading is being taken, no current is drawn from the source to…
Concave Mirror Focal Length by u-v Method :- Concave mirrors have the reflecting surface that bulges inward. They are also called converging mirrors because it converges all parallel beam of light incident on it. Unlike a flat mirror, concave mirrors can form real images that are projected out in front of the mirror at the place where the light focuses. Concave mirrors can be used in satellite dishes, vehicle headlights, astronomical telescopes and many more areas. The relation between object distance u and the image v from the pole of the mirror is given by, 1/v + 1/u = 1/f…
A convex mirror is a curved mirror in which the reflecting surface bulges towards the light source. Convex mirrors reflect light outwards; therefore they are not used to focus light. A convex mirror is also known as fish eye mirror or diverging mirror. The image formed by a convex lens is virtual and erect, since the focal point (F) and the centre of curvature (2F) are both imaginary points “inside” the mirror that cannot be reached. As a result, images formed by these mirrors cannot be projected on a screen, since the image is inside the mirror. Therefore, its focal…
A concave lens is thinner at the center that at the edges. So the light beams passing through the lens are spread out or diverged. Therefore, the concave lens is called a diverging lens. The image formed by a concave lens is virtual and diminished. Since a concave lens will not produce a real image, a convex lens is used to measure its focal length. There are two methods to find the focal length of a concave lens: (a) Lens in Contact Method and (b) Lens out of Contact Method. This video explains how find the focal length of…
Diode is a two terminal P-N junction device. P-N junction is formed by bringing a P type material in contact with N type material. Diode is unidirectional device that allows the flow of current in one direction only depending on the biasing. When P- terminal connected to positive terminal of battery and N-terminal connected to negative terminal of battery, it is said to be forward biased. In reverse biasing P- terminal is connected to negative terminal of the battery and N- terminal to positive terminal of battery. A diode characteristic is simply a graph of the voltage applied to…
The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The Vernier Caliper consists of a main scale fitted with a jaw at one end. Another jaw, containing the vernier scale, moves over the main scale. When the two jaws are in contact, the zero of the main scale and the zero of the Vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error. This video explains how to find the volume of a small sphere, cylinder, beaker and a…
A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. There are two types of transistor characteristics: (i) Input characteristics and (ii) Output characteristics. Input characteristics have different constant values of collector voltages (VCE), and are represented by…
Emulsions are an important class of the colloidal system. It is a liquid-liquid colloidal system in which the dispersed phase and dispersion medium are liquids. Emulsions are a mixture of two or more immiscible liquids that are normally immiscible. They have the property to scatter the light passed through them, called Tyndall effect. If the emulsion scatters all light equally, it becomes white. If the emulsion is dilute, the low wavelength light will be scattered more and it becomes bluer and if it is more concentrated, the longer wavelength light will be more scattered and emulsion becomes more yellow. …
Gaseous state is a state of matter in which the substance does not have any specific shape or volume. It adopts the form and size of its container. The fundamental macroscopic properties of gases are pressure, volume, temperature and mass of the gas. The relationships among pressure, temperature and volume of a gas lead to Gas laws. According to Boyle’s Law, the pressure (P) of a given mass of gas is inversely proportional to its volume (V), provided that the temperature of the gas remains constant. i.e, the volume of gas increases as the pressure decreases. This video explains…
Chemical equilibrium is the condition which occurs when the concentration of reactants and products participating in a chemical reaction exhibit no net change over time. It is also be called a “steady state reaction.” which means ,the consumption and formation of substances has reached a balanced condition and the quantities of reactants and products have achieved a constant ratio, but they are almost never equal. This video explains how to study the shift of equilibrium between ferric ions and thiocyanate ions by increasing the concentration of either of them.
Pollution is the addition of any substances into the natural environment that makes it harmful to humans, animals and plants. Substances that cause pollution to the environment are called pollutants. Pollutants can be either foreign substances/energies or naturally occurring contaminants. Air pollution is the contamination of the air, by the introduction of particulates, smoke or harmful gases into the atmosphere. Some air pollutants are poisonous, which makes it difficult for plants, animals and humans to survive. The atmosphere in highly populated areas are very rich in dust, smoke and suspended particulate matter, all due to vehicular exhausts and industrial emission….
The rate of a chemical reaction may depend on the concentration of one or more reactants or it may be independent of the concentration of a given reactant. The effect of concentration of the reactant on the rate of a chemical reaction can be studied by analysing the reaction between potassium iodate and sodium sulphite in presence of starch indicator at room temperature and pressure.. In acidic medium, potassium iodate is reduced to iodide ions by sodium sulphite. Iodide ions formed are oxidized to iodine by reaction with more iodate ions. The liberated iodine reacts immediately with sulphite ions forming…
An electric circuit is simply a closed loop through which charges can continuously move. An electric circuit basically contains a source of electricity, a load resistance, a switch or a key for turning the circuit on or off at one’s convenience. If the starting ends of two resistors are joined to a point, and the terminal ends of the two are combined and given connection to a source of electricity, those circuits are called Parallel Circuit. Unlike in the series circuit, the current in each branch of a parallel circuit will be different. If one branch is broken, current will…
Urea is present mainly in the urine of all mammals, but it also occurs in blood, bile and milk. Urea is naturally produced during the process of breakdown of proteins. Due to this process, amino groups are removed from the amino acid present in the proteins. These amino groups are converted to highly toxic ammonia (NH3), and the ammonia thus produced is finally converted to urea by the liver. The urea thus formed then passes to the kidneys and is finally excreted from the body through the urine. This video explains how to detect the presence of urea in…
Flowers, the reproductive organs of all plants, distinguish flowering plants (angiosperms) from seed plants (gymnosperms). Flowers that contain either male or female parts are called imperfect, while those with both are called perfect flowers. The stamen is the male reproductive part that is comprised of a yellow anther that features a sac full of pollen, and the delicate, long stem it rests on, called the filament. The female reproductive part is the pistil that is usually found in the center of a flower. It is comprised of three parts–the upper sticky part that catches and traps pollen is the stigma;…
Lead is a soft grey metal. It is used in shots and weights. Lead is found in many salts like lead chloride and lead sulphate as lead (II) ion. In group II, lead (II) ions are precipitated as their sulphides by passing hydrogen sulphide gas through their solution. Lead (II) ions on reaction with conc. nitric acid and sulphuric acid to form a white precipitate of lead acetate. These ions also form yellow precipitate of lead iodide and lead chromate on reaction with potassium iodide and potassium chromate respectively. This video explains how to test for the presence of…
In organic chemistry, there are saturated and unsaturated organic compounds. Saturated compounds contain chain of carbon atoms linked together by single bonds. Alkanes are examples of saturated compounds. Unsaturated compounds contain carbon – carbon double or triple bonds such as those found in alkenes and alkynes. This video explains how to detect the presence of unsaturation in an organic compound using some simple tests.
Iron is a chemical element with symbol Fe. Iron is in +3 oxidation sate is called ferric ion. It is found in salt like ferric chloride. In group III, ferric ion is precipitated as its hydroxide by adding ammonium hydroxide to its solution. The reddish brown precipitate of ferric hydroxide is dissolved in HCl due to the formation of soluble ferric chloride. Ferric chloride reacts with potassium ferrocyanide to form prussian blue coloured Ferric ferrocyanide and potassium sulphocyanide to form blood red coloured Ferric sulphocyanide. This video explains how to test for the presence of ferric ion in a…
Cobalt is a chemical element with symbol Co. It is found in various salts like cobalt chloride, cobalt nitrate and cobalt carbonate as Co (II) ion. Cobalt based blue pigments, cobalt blue, have been used for jewellery and paints and to impart distinctive blue tint to glass. In group IV, cobalt ions are precipitated as their sulphides by passing hydrogen sulphide gas through their solution. Cobalt ion reacts with potassium nitrite in presence of acetic acid to form yellow precipitate of Potassium cobaltinitrite. It also reacts with ether and a crystal of ammonium thiocyanate, to form blue coloured ammonium cobalti…
Starch is the most common carbohydrate in the human diet and is contained in many staple foods. The major sources of starch intake worldwide are cereals (rice, wheat, and maize) and root vegetables (potatoes and cassava). We can use iodine solution to test for the presence of starch. If starch is present is a food item, it turns blue-black colour when iodine solution is added to it. This video explains how to test for the presence of starch in a given food sample.