11.

A linear object is placed on the axis of a lens. An image is formed by formed by refraction in the lens. For all the positions of the object on the axis of the lens, the positions of the image are always between the lens and the object.

i) Name the lens

ii) Draw a ray diagram to show the formation of the image of an object placed in front of the lens at any position of your choice except infinity.

A radar sends a signal to an aeroplane at a distance of 45 km away with a speed of 3 x 10⁸ m/s. After how long is the signal received back from the aeroplane?

i) What is meant by an echo? Mention one important condition that is necessary for an echo to be heard distinctly.

ii) Mention one important use of echo.

i) Sketch a graph to show the change in potential difference across the ends of an ohmic resistor and the current flowing in it. Label the axes of your graph.

Three resistors of 6 ohm, 2 ohm and 4 ohm respectively are joined together as shown in the figure. The resistors are connected to an ammeter and to a cell of e.m.f 6 V. Calculate:

Draw a labeled diagram of the staircase wiring for a dual control switch showing a bulb in the circuit. 

The electrical gadgets used in a house as bulbs, fans, heater etc. are always connected in parallel, not in series. Give two reasons for connecting them in parallel.

An electrical heater is rated 4 kW, 220 V. Find the cost of using this heater for 12 hours if one kWh of electrical energy costs Rs. 3.25? 

State one point of similarity and one point of difference between an a.c. generator and a d.c. motor?

i) What is the name given to a cylindrical coil whose diameter is less in comparison to its length?

ii) If a piece of soft iron is placed inside the current carrying coil, what is the name given to the device.