Q: 41. The number of electrical generators used in areas where small workshops existed created lot of pollution. Rishab and his five friends did a survey and realized that like in multistoried apartments, a common generator could be set up for all these small workshops so that the noise and air pollution could be reduced considerably. They had a tough time convincing the local bodies and now they are going to the NGOs and some financiers to help them organize funds to do the needful. It is admirable to see their perseverance.
∎ What values did Rishab and his friends have?
∎ Kamla pedals a stationary bicycle, the pedals of which are attached to a 100 turn coil of area 0.10 sqmetres. The coil rotates at half a revolution per second and is placed in a uniform magnetic field of 0.01 Tesla perpendiculars to the axis of rotation of the coil. What is the maximum voltage generated in the coil?
Q: 42.Alka and her sister were watching a movie in which the phenomena of aurora boriolis was shown. Alka could not believe her eyes that such a colorful display like the one during commonwealth games could be created by nature. She went to the library, but could not find the right book. So she consulted her teacher who guided her. Hence, Alka understood that during a solar flare, a large number of electrons and protons are ejected from the sun. Some of these get trapped in the earth’s magnetic field and move in a helical path along the field lines. As the density of the field lines increases near the poles , these particles collide with atoms and molecules of the atmosphere emitting green and pink light. Alka shared this knowledge with her class when they studied the chapter of moving charges in magnetic field.
∎ What values did Alka have?
∎ What is the radius of the path of an electron moving at a speed of 3 × 107 m / sec in a magnetic field of 6 Gauss perpendicular to it? What is its frequency ? Calculate its energy in kilo electron volt.
Q: 43. Renu saw her aunt suffering from severe joint pain. Her aunt could not take any pain killer as she was allergic to them. Renu in her quest to help her aunt found the use of magnets. She read Dr. Philpott’s work on magnetic therapy, that most people are negative magnetic field deficient due to electromagnetic pollution. Supplementing the body with negative field energy has shown to restore balance and encourage healing. Renu takes her aunt to the doctor daily without fail for the treatment.Her aunt is improving at a phenomenal speed.
(i) What values does Renu have?
(ii) A short bar magnet has a magnetic moment of 0.48J/T. Give the direction and magnitude of the magnetic field produced by the magnet at a distance of 10cm from the centre of the magnet on a) axial line b) the equatorial line of the magnet.
Q: 44. Raju was enjoying TV programme at his home with his family at night. Suddenly the light went off causing darkness all over. Mother asked Raju to bring candle along with matchstick from kitchen to put the TV switch off. Raju at once picked the mobile phone and pressed the button lighting up the surrounding. Her mother was surprised and asked where from the light was coming. Raj proudly showed her the mobile.
∎ Which valueis displayed by Raju ?
∎ Which material is used in LED ?
Q: 45. Garima and Gaurav want to purchase a new TV set. They visited electronic shops to look for some branded TV. The dealer showed them LCD and LED TV, s. Now they were confused which set to buy. Finally after discussing with friends, reading relevant literature and searching the internet, they decided to purchase LED.
∎ Which value is being highlighted I by Garima and Gaurav?
∎ What is the difference between LED and LCD?
Q: 46. Vikas was reading semi conductor in physics. His teacher has explained that electronic components operate at very low voltage. But at home he daily saw his father using wall socket for charging mobile.(220V) Confused Vikas put his doubt in front of his teacher and was satisfied. Next day he went to school and shared the information with his classmates.
∎ Name the values displayed by Vikas ?
∎ What is the principle of charger?