The advantages and limitations of electron microscopy.
The advantages and limitations of electron microscopy There are two main branches of microscopy that are pertinent to cell biology. These branches arise from the two types of microscope; the light microscope and the electron microscope. The basic principles of light microscopy have been known since circa 17th century, however improvements in lens manufacture in circa 19th century allowed the use of microscopy to be much more practically available and useful. This is increased ability inspired rapid research into both the design of microscopes and the preparation of specimens. However, the light microscope can only magnify objects bigger than 0.2 micrometres; due to its limited resolving powers. This is because it utilises a beam of light. Relatively, light has a long wavelength, this means that when there are two small points close together there is too much refraction and wave front overlap, the eye then only sees one point. This can also be considered in terms of objects "crossing the path" of the wavelength. The smallest wavelength of visible light is 400nm, the diameter of mitochondria is 1000nm, and therefore mitochondria cross the path of the light wave. However ribosomes have a diameter of 22nm, and do not cross the path of the light wave and are therefore not seen by the light microscope. As biologists came to realise these limitations they understood that the
investigating the relationship between the diameter and the current in a wire at its melting point
Investigation Report Aim Theory Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens. Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. Some formulae for resistance are where R is the resistance of the object / ? V is the potential difference across the object / V I is the current passing through the object / A (Ref. http://en.wikipedia.org/wiki/Electrical_resistance) where R is the resistance/ ? ? is the resistivity / ?m l is the length of the wire / m A is the cross section area of the wire / m A = ?() = ? where A is area / m d is the diameter / m Putting the formulae together, so (Ref. http://physics.bu.edu/~duffy/PY106/Resistance.html) Aim of investigation The aim of this work is to investigate the relationship between the resistance and the diameter of the wire. Variables Variable Independent / Controlled / Dependent Resistance D Resistivity C Length of wire C Diameter I Prediction Since the theory suggests that So So the resistance should be
Experiment to measure deflection when a force is applied to a cantilever.
Sc1 Investigation - bending of a Cantilever. Experiment to measure deflection when a force is applied to a cantilever. Introductory Diagram Aim To find out whether varying the load has any affect on the deflection (?d) of the ruler. Theory Elasticity is the property, which allows a material to regain its shape after being distorted. Some materials like, rubber bands, are much more elastic than others. The elastic limit of a material is the maximum amount by which it can be stretched and still regain its original shape after the distorting forces are removed. If a material is stretched beyond its elastic limit its shape is permanently changed. ' The deformation of a material is proportional to the force is applied to it, provided the elastic limit is not exceeded'. This is known as Hooke's Law, named after its discoverer, Robert Hooke, a 17th century scientist. Young's Modulus When stress is applied to a material, strain is produced in the material. The strain is proportional to the stress, provided the stress does not exceed a limit known simply as the 'limit of proportionality'. Within this limit, the value of is a constant for that material, and is known as the Young Modulus for the material. The Young Modulus (E) = Provided the limit of proportionality is not exceeded. Before we can work out the Young Modulus we need to know about stress and strain.
Force of friction
Kwun Tong Government Secondary School Advanced Level Physics (TAS) Experiment Report Experiment No.: 1 Title: Force of friction Date of Experiment: 2006/10/31 Mark: Sch. Code 2114 TAS Group 5 Name: Chan Man Lok Class: S.6C Class No.: 6 Objective: . To study the effects of the normal force, and surface area on the force of friction using a block. 2. To estimate the coefficients of static and kinetic friction. Apparatus: Instrument Description Wooden block x 4 200g x 4 Spring balance x 1 DCS/PL/2-2 0 - 10N The smallest division = 0.2 N Tripe beam balance x 1 0 - 500g The smallest division = 0.1g Frictional paper x 1 / Rubber band Several / Theory: Limiting static friction : Friction always opposes motion. Larger forces tending to produce the motion, larger friction is. However, it cannot increase indefinitely. For example, when a body is in contact with a rough surface frictional forces arise at the contact surface if the body is subjected to an applied force. When the applied force exceeds the limiting static friction , the body will start to slip over the rough surface. And the value of is roughly proportional to the normal force R. where is the coefficient of static friction at maximum at the contact surface. Kinetic friction : However, the friction acting on a resting block
Ice Lab and its Phase Changes
Lab 1: Ice Lab and its phase change Introduction: Everything is made up of matter. It has shape, volume and mass. All one hundred and nine elements have three states and provide the world with daily activities. An element at a solid state has particles that are very close together and vibrate. A solid state has a set shape, mass and volume and this gives it a tough shape. The second state of an element is a liquid and it also has a set volume and mass. In this state the particles vibrate and rotate in a limited space. However, like the solid they do not have a rigid shape, liquids are shaped liked the object in which they are poured. The last state of the elements is a gas. Particles of gas are very free and can vibrate, rotate, move rapidly, and the shape of gas is not known. These three states are very amusing when one experiments and looks at the changes from one phase to another. In addition, when one state changes from solid to liquid, the particles move more rapidly and the energy is more increased. This causes solid to change to a liquid form or state. The temperature remains constant as the phase changes. As more energy is increased or heat is delivered to the particles it causes the liquid to change its shape to gas. This is known as the process of phase change. When you are going from liquid to solid, the energy of the particles decreases and there is less
How the resistance of an ammeter changed when introduced into a circuit.
DC MEASUREMENTS The experiment was to find out how the resistance of both an ammeter and voltmeter, using both an ammeter and voltmeter changed when introduced into a circuit. From doing this it was found that the resistance of the ammeter decreases as both the emf and current decrease, however the avometer suggested that internal resistance increases with the voltage. Introduction Voltmeter's and ammeter's use a moving coil galvanometer to take the current and a mechanical pointer to display the current. When using analogue components an important factor to consider is full-scale deflection, which is when the maximum deflection of an analogue instrument such as a moving coil meter is reached. At present the full-scale deflection of most instruments is 10-50 ?A, but to overcome this shunting resistors are placed in parallel to carry the excess current. To take the voltage of an object, the shunting resistor must be placed in series, as the resistance of the moving-coil galvanometer is not very high. Some formulae which may be useful during this experiment is: Method The experiment firstly started by looking at calculating the resistance of the voltmeter. This was done by setting the circuit up as below: E = d.c. power supply M = Voltmeter being tested Rm = Voltmeter resistance I = Current The avometer was then placed upon successive ranges of 3v, 10v, 30v,
A Separate Peace by John Knowles - summary of theme and narrative
A Separate Peace One should never do such a thing; that when looking back in life they should repent it. A Separate Peace is a flashback novel, written by John Knowles. It takes place in the 1940's in an all male boarding school in New Hampshire. Gene, a fairly young man now visits his old high school, Devon High School fifteen years after graduation, remembering mainly his summer before and his last year there. Gene had spent his time there with his "best friend" Finny. Finny was the time of guy that could get away with everything and anything, especially during the Summer Session the boys were attending. He was good at almost everything, well except for academics. Gene no doubt was the smart one of the two, while Finny was athletically strong. To understand the many feelings and actions that the characters go through, the setting should be taken into great consideration. The 1940's; World War two was taking place at that time. Men from all over the country were getting drafted. At the end of this year, these boys would also be drafted, fighting a war that their families, neighbors, teachers, and fellow citizens were already fighting. Once the Summer Session finishes these boys will begin senior year, at the end of which they will be sent away. Amidst all this confusion and free there is a pair of boys, Finny and Gene. Finny was intimidating, basically everything he said
I am going to investigate respiration in crickets and how temperature varies the rate of respiration.
Planning I am going to investigate respiration in crickets and how temperature varies the rate of respiration. The calculation for aerobic respiration is: Oxygen + Glucose Carbon dioxide + water + energy 6O2 + C6H12O6 6CO2 +6H2O + (J) I will do the experiment safely by making sure that the water will not be too hot or too cold, this is a safety precaution for me as well as the crickets. As we don't want to cause the crickets too much distress or pain. It will be a fair test and accurate because I will: * Use the same crickets * Same mass of crickets * Let the crickets return to room temperature * Reset the measuring device after each experiment * Do each experiment 3 times to get an average I predict that the lower the temperature the lower the rate of respiration. Equipment list: * 2 beakers- a lager one that will hold the different temperatures of water, a smaller one to hold the ink marker. * Crickets- to test on * Bung- containing delivery tube and waste (reset) tube * Ink- to mark distance on the scale * Delivery tube with scale on- to mark distance * CO2 remover- to remove the CO2 * Excess tube for reset. I will measure the amount of oxygen used by the crickets by measuring how far the ink marker has traveled up the scale, the rate of respiration at different temperatures and conditions. The variables that affect the rate of
Investigating the depression of a ruler when force is applied.
Investigating the depression of a ruler when force is applied Investigation: Measuring the depression of a ruler when force is acted upon it and when the length of overhang is altered. Planning First of all it was important before starting anything that the environment where the experiment was taking place was a safe one and that I was not in any danger whilst doing my investigation. I will make sure that the desk is clear with only the required apparatus present and also make sure that no more weight than 6N is put on the ruler otherwise it might snap and a splinter could come up into my eye. There are three independent variables in this experiment. These are the over-hang of the ruler, the mass added to the ruler and where the mass is positioned on the ruler. I will be investigating two of these independent variables, which are the alteration in overhang and the mass added to the end of the ruler. These will then produce a Dependant variable. This is the amount the ruler bends. For this experiment I will set up a one-meter ruler lying horizontally off the side of the work desk with a block of wood on top of it and a G Clamp holding it in place so it does not move. I will then add individual weights of 1 Newton to a piece of string hanging on the end of the overhanging ruler. I will measure the distance that the ruler has bent by using another ruler lying vertically
physics investigation- stopping distance
Physics Investigation Introduction In my investigation I intend to gather enough evidence and explanation to see if and how the mass of a ball will affect its stopping distance. I will carry out a series of tests starting with changing the mass of the ball then changing height which it's dropped from. Predictions I predict that the mass of a ball will most defiantly affect the distance it takes to stop because as the mass increases, the amount of friction with the surface will increase which will slow down the ball sooner. I believe if the mass of the ball is doubled the friction with the surface it's on will double and therefore half the distance taken to stop. Equipment For my investigation the equipment I will require is: * A ramp and stand ( 1 metre long) * Carpet (2 by 0.5 metres) * 2 balls of different masses but same size ( ball 1, 2.8g and ball 2, 44.9g) * 2 metre rules My setup My setup is pretty simple I will use a ramp with a rule along it and some carpet for the balls to roll along I will then use another rule to measure the distance taken to stop. When I first set up my equipment the balls where rolling around everywhere, to overcome this problem I decided to curl the carpet into a half bowl shape the balls then rolled smoothly down the ramp and along the carpet. Procedure Firstly I will drop the lighter ball 1, and measure its stopping distance
