Your Science board exam is on March 28. So, we got Topper Physics expert Leena Garg to clarify your doubts! Here is the transcript for those who missed the chat:
Gurman Bhatia: Can you please tell the differences between a/c current and d/c current
Leena Garg: DC current flows in only one direction. AC current keeps reversing the direction. But in the household supply this happens at an extremely fast rate, so the bulb seems lit at all times.
NITISH AGARWAL: What all we need to know for ac/dc generators/motors as most of it is not in syllabus?
Leena Garg: Learn the principle of both.
dazzling neeraja: name any two elements that are used in fabricating solar cells
Leena Garg: Silicon and germanium are used in solar cells.
swati: while drawing the ray diagrams for concave mirror or convex lens when the object is at C i do not get the image at C or the size of the image is not the same as the object.why?
Leena Garg: Draw a more accurate ray diagram. Use a pencil and scale to draw the lines. Don't forget to sharpen your pencil as that will give you a more accurate image. Use a compass to draw a lens and take a straight line in the middle of the lens. Draw rays up to this line.
Pranav Gupta: What is presbyopia? Is it a combination of Myopia and Hypermetropia?
Leena Garg: No, presbyopia is age-related hypermetropia. When your grandfather reads the paper by holding it at a distance, you know that he is suffering from hypermetropia which in his case is called presbyopia.
deepitapai: what does deliquescent nature of NaOH & KOH mean?
Leena Garg: Deliquescent nature of NaOH and KOH means that when these compounds are left open in air. They absorb moisture from air and become wet.
minhaja: can u pls..tell me the brief explanation hou 2 find the position of elements in periodic table.......??
Leena Garg: You need to learn the modern periodic table. First 20 elements should be learnt very well. The modern periodic table consists of periods and groups. A particular element belongs to a specific group and period.
Vatsal Agarwal: In a question where they ask u 2 complete a diagram,where a prism is given & a light ray falls on it,do we show the spectrum formation or the other diagram(the one showing the normal, refracted & emergent ray, etc) ?
Leena Garg: If the question asks you to show dispersion of light, draw the spectrum. If it asks you to mark the angle of deviation of the ray draw the angle between the incident ray and emergent ray.
aakanksha ag: Mam please tabulate diff between an electromagnet and permanent magnet. Please give def of electromagnet also.
Leena Garg: Stretch the fingers of your right hand so that they are perpendicular to each other. Then the first Finger points in the direction of the field and thuMb is in the direction of motion then second finger gives the current. Note the cap letters are to remember the quantity that the finger points to. Normally you are asked to state the direction of the current say north, south, east ,west or up and down.
deepitapai: can we be asked to solve numericals based on ph??...
Leena Garg: Simple questions based on pH could be asked in your exam. Like you can be given the pH of a solution and you can be asked to predict whether it is neutral, basic or acidic.
Gowthami: Good Afternoon Ma'am!...Can u please make my concepts clear on the numerical questions regarding the eye defects....My confusion is that why do we take the value of 'v' as negative when our eye lens is convex and the image formed on the retina is real and inverted? Shouldn't it be taken as positive? ....And also is electric motor and generator been deleted out of our portions? ... I will be extremely grateful for your guidance...Thanking you,Gowthami!=):D
Leena Garg: Hello Gowthami. The sign of the image distance v does not depend on the nature of the lens forming the image. It depends on whether the image is formed in front of the lens or behind the lens. For generator and motor you just read the principle of these two. Practice more with these Mock Papers
mangalam: whts the simplest way to learn the modern peroidic table???
Leena Garg: Learn the first 20 elements with their atomic number. It will be then easy for you because those are most important. Learn them along with symbols.
deepitapai: When asked to draw electronic dot structure of various carbon compounds,can we draw it in the other way by drawing lines...?....because im unable to understand as to how we should draw electronic dot structure.
Leena Garg: No, electron dot structures should always be drawn by using dots and crosses. Try practicing some structures and it will be clear to you. Practice more with these Mock Papers
minhaja: is checker box and blood group asked in board exam......?bcoz i feel it vry tough........
Leena Garg: Dear M, well as the topic is mentioned in the CBSE syllabus, it could be asked in your exam.
swati: In numericles for myopia or hypermetropia what r the value of u & v?
Leena Garg: In numericals for the eye, u and v both are always negative. This is because the object and image are on the same side of the lens.
Sanket Wani: What is the magnitude of current through a voltmeter and an ammeter?
Leena Garg: A voltmeter measures the potential difference or the voltage. Ammeter measures the current.
deepitapai: can we be asked to balance ionic equations?
Leena Garg: No, balancing of ionic equations is not in the course.
gilbertraichur: WHAT IS COUPLE (force acting in AC DC MOTAR)
Leena Garg: It is the product of either of the forces and the perpendicular distance between them.
srinidhi: What is a myphoic eye and a hyper metrophic eye? Please answer maam.
Leena Garg: A person is suffering from myopia when he cannot see distant objects. The rays converge in front of the retina. If a person suffers from hypermetropia he cannot see object placed close by. The rays converge beyond the retina.
divyanshu: what is magnetic flux?
Leena Garg: It is the number of field lines crossing an area.
Ahmed: hi....could u give some important points from the chapter carbon and it's compounds.
Leena Garg: When studying carbon and its compounds, study all the rules for nomenclature carefully. Remember the prefixes and suffixes used. Also study the types of reactions like addition, substitution. Study the properties of ethanol and ethanoic acid.
divyanshu: mem,how can we know the nature,size and position of images formed by concave and convex mirror?
Leena Garg: Hello After solving a numerical you look at the image position, that tells you whether it is a real or virtual image. If the image is negative then it is a virtual image and if its value is positive then it is a real image. Next find the magnification using m = -v/u. That gives you the size of the image and if the magnification is more than 1 the image is magnified, else it is diminished.
aakanksha: mam please tell me how to find directions using right hand thumb rule?? how do we mark them on paper??
Leena Garg: Stretch the fingers of your right hand so that they are perpendicular to each other. Then the first Finger points in the direction of the field and thuMb is in the direction of motion then seCond finger gives the current. Note the cap letters are to remember the quantity that the finger points to. Normally you are asked to state the direction of the current say north, south, east ,west or up and down.
aakanksha:mam, please name some devices that give AC current and some which give DC current.
Leena Garg: An ac generator generates AC current and a dc generator produces dc current.
Meghana.S: What is hydronium ion? Does H+(aq)mean the same?
Leena Garg: Hydronium ion is H3O+. It is formed when H+ ion reacts with H2O. H+ ion is hydrogen ion and not hydronium ion. Hydrogen ion after reacting with water forms hydronium ions.
minhaaj: hi....... wen i c lens diagrams i cant able to study......im scared of diagrams. can u pls tell hou 2 overcome this problem.......?
Leena Garg: Practice the ray diagrams given in the book. Do question with the diagram at the end. By then you are a little comfortable as you have attempted the other questions, keep calm and just attempt it patiently.
aman gandhi: Hi could u please tell me an element whose resistance is almost unchanged with increase in temperature.
Leena Garg: Constantan, nichrome.
