Current Electricity quiz

The SI unit of resistivity is:

The drift velocity of electrons in a metal wire is typically of the order of:

The resistance of a metallic conductor with rise in temperature:

Kirchhoff's junction rule is based on conservation of:

When cells are connected in series, the total emf is:

The balance condition of a Wheatstone bridge is:

The SI unit of mobility is:

A material whose resistance changes very little with temperature, used in standard resistors, is:

The power dissipated in a resistor R with voltage V across it is:

Kirchhoff's loop rule is based on conservation of:

Why is the terminal voltage of a cell less than its emf when it supplies current? (2 marks)

How does the drift velocity change if the length of a wire is doubled at constant potential difference? (2 marks)

Why is nichrome used in heating elements? (2 marks)

Why does the resistivity of a semiconductor decrease with temperature? (2 marks)

Write the relation between current and drift velocity, naming each symbol. (2 marks)

Why are household appliances connected in parallel? (2 marks)

Derive the relation between resistivity and relaxation time. (2 marks)

Two wires of the same material and length have areas in the ratio 1:2. Find the ratio of their resistances. (2 marks)

What is a non-ohmic device? Give one example. (2 marks)

When is the terminal voltage of a cell greater than its emf? (2 marks)

A current of 2 A flows through a wire for 5 minutes. Find the charge that passes and the number of electrons (e = 1.6 x 10^-19 C). (3 marks)

Three resistors of 2 ohm, 4 ohm and 6 ohm are connected (i) in series and (ii) in parallel. Find the equivalent resistance in each case. (3 marks)

A cell of emf 1.5 V and internal resistance 0.5 ohm is connected to a 2.5 ohm resistor. Find the current and the terminal voltage. (3 marks)

An electric heater is rated 1,000 W, 220 V. Find its resistance and the current it draws. Find the cost of using it for 2 hours at Rs 8 per kWh. (3 marks)

A wire of resistance 10 ohm is stretched uniformly to twice its length. Find its new resistance and state whether its resistivity changes. (3 marks)

Read the passage and answer the questions. A house uses four 100 W bulbs, two 60 W fans and a 1,500 W air conditioner, all for 5 hours a day, on a 220 V supply. (i) Find the total power when all are on. (ii) Find the daily energy consumption in kWh. (iii) Find the current drawn and suggest a suitable fuse rating. (5 marks)

Read the passage and answer the questions. A storage battery of emf 8.0 V and internal resistance 0.5 ohm is being charged by a 120 V DC supply through a series resistor of 15.5 ohm. (i) Find the charging current. (ii) Find the terminal voltage of the battery during charging. (iii) Why is the series resistor necessary? (5 marks)

Read the passage and answer the questions. An electrician uses thick copper wires for house wiring and thin nichrome wire for the element of an electric iron. (i) Why is copper used for wiring? (ii) Why is nichrome used for the element? (iii) Why are the house wires thick? (5 marks)

Read the passage and answer the questions. A weighing machine uses a strain gauge, whose resistance changes when stretched, as one arm of a Wheatstone bridge. With no load the galvanometer shows zero deflection. (i) What is the condition of the bridge with no load? (ii) What happens when a load is placed? (iii) Why is the Wheatstone bridge sensitive for such measurements? (5 marks)

Read the passage and answer the questions. A platinum resistance thermometer has a resistance of 100 ohm at 0 degree C. The temperature coefficient of platinum is 0.0039 per degree C. (i) Write the relation between resistance and temperature. (ii) Find its resistance at 50 degree C. (iii) Find the temperature when its resistance is 139 ohm. (5 marks)

Derive the relation I = neAvd and use it to derive Ohm's law, obtaining an expression for resistivity in terms of relaxation time. (6 marks)

State Kirchhoff's rules and use them to derive the balance condition of a Wheatstone bridge, with a circuit diagram. (6 marks)

Derive expressions for the equivalent emf and internal resistance of two cells connected (i) in series and (ii) in parallel. (6 marks)

Explain the variation of resistivity with temperature for metals, alloys and semiconductors, with graphs and reasons. (6 marks)

Explain the limitations of Ohm's law with I-V graphs of non-ohmic devices, including a device whose current depends on direction of voltage and one with negative resistance region. (6 marks)