I WANT PHYSICS

  The correct statements are:i) Low temperature at poles cause air to contract. ii) High temperatures along equator cause air to expand.When temperature decreases, air contracts and becomes denser. When temperature increases, air expands and becomes less dense from Preeti Khosla

  TYPES OF CONNECTIONS: Electric components can be connected in two ways SERIES:   When negative terminal of first component is connected to positive terminal of second component, negative terminal of second component is connected to positive terminal of third component and so on, then the components are said to be connected in series. PARALLEL:   when the positive terminals of all the components are connected to one end and the negative terminals of all the components are connected to another end, then the components are said to be connected in parallel. HOW TO FIND EQUIVALENT RESISTANCE OF COMBINATION OF RESISTORS CONNECTED IN SERIES AND PARALLEL? RESISTORS CONNECTED IN SERIES: In series connection of resistors there is only one path for the flow of current in the circuit. Hence, the current in the circuit is equal to i. But potential difference varies depending upon the resistance of a resistor. According to Ohm’s law, Potential difference across R 1 is , V 1 = iR 1 Potential dif

 OHM’S LAW Before going to Ohm’s law let us discuss in brief about some electrical components or devices we use in electric circuits.    A Battery serves as a source of electricity in a circuit. We use mainly two measuring devices in this concept those are  Volt meter: used to measure potential difference between the two ends of a conductor. So it is always connected in parallel ( we learn about types of connections later in this chapter) Ammeter: used to measure the current passing in the circuit. So it is always connected in series. Now let us dive in to the activity did by Ohm to understand his concept. Materials required: 5 dry cells of 1.5V each, conducting wires, an ammeter, a volt meter, thin iron spoke of length 10cm, LED and key.   Procedure: Connect a circuit as shown in the above figure. Solder the conducting wires to the ends of the iron spoke. Close the key. Note the readings of current from ammeter and potential difference from volt meter in table     Now connect two cell

  WORKING OF BATTERY: A battery consists of two metal plates (electrodes) and a chemical (electrolyte). The electrolyte (chemical) between the two metal plates consists of positive and negative ions which move in opposite directions The electrolyte exerts a certain force on these ions and makes them move in a specified direction. Let us call this force as a chemical force (Fc). Depending upon the nature of the chemical, positive ions move towards one of the plates and accumulate on that plate.   As a result of this accumulation of charges on this plate it becomes positively charged (called anode). Negative ions move in a direction opposite to the motion of positive ions and accumulate on the other plate. As a result of this the plate becomes negatively charged (called cathode). This accumulation of different charges on respective plates continues till both plates are sufficiently charged.          But the ions in motion experience another force , when sufficient number of charges are a

  POTENTIAL DIFFERENCE: When the ends of a conducting wire are connected to the terminals of a battery, an electric field is setup throughout the conductor. This field exerts a force on the charge (electron). Let Fe be the force exerted by the electric field on a free charge q. The free charges accelerate in the direction of the electric field (If the free charges are electrons, then the direction of electric force on them is opposite to the direction of electric field). It means the electric field does some work to move free charges in a specified direction.                                Let the electric force made the charges move through a distance ‘l’ from A to B as shown in figure . We know that, the work is the product of force and distance along the direction of force. Hence, work done by the electric force on a free charge q is given by W = Fe l   [since work is the product of force and displacement] Work done by the electric force on unit charge = W/q = Fe l/q “Work done by t

INTRODUCTION TO ELECTRICITY ELECTRICITY: Electricity is a branch of physics which deals with study of charges. The property of matter that is responsible for electrical phenomena is called charge. Electricity is further divided into two sub branches. They are: 1)     Static electricity: the study of charges which are at rest. And 2)     Current electricity: study of charges under motion. This is what we are also calling as electric current. In terms of electric current materials are classified into three types: 1)     Conductors: the materials which can able to allow electric current to pass through them. Eg: all metals, water with salts and minerals, etc. 2)     Insulators: the materials which cannot able to allow electric current to pass through them. Eg: wood, plastic, rubber, etc. 3)     Semi conductors: the materials which cannot allow electric current freely as conductors. These materials can able to allow only a partial current to flow slowly through them. Eg: silicon, germanium

 HUMAN EYE AND COLOURFUL WORLD EXAMPLE QUESTIONS:   1  1)  Light of wavelength λ 1 enters a medium with refractive index n 2 from a medium with refractive index n 1 . What is the wavelength of light in second medium? ANS:   we know, refractive index is inversely proportional to wavelength.             n∞1/ λ ð n 1 /n 2 = λ 2 / λ 1 ð λ 2 =n 1 λ 1 /n 2   2  2)   If a white sheet of paper is stained with oil, the paper turns transparent. Why? ANS: we can get so many answers for this question because there may be multiple reasons for this. But i will suggest one best answer for this. A white sheet of paper consists of cellulose. The refractive index of cellulose is very near to the refractive index of oil. so, it turns transparent.   3    3)  A light ray falls on one of the faces of a prism at an angle 40 o so that it suffers angle of minimum deviation of 30 o . Find the angle of prism and angle of refraction at the given surface. ANS: To answer this quest