A wire that has resistance R is cut into two equal pieces. The two parts are joined in parallel. What is the resistance of the combination ?
Resistance of each part is R/2.
Resultant resistance R’ is given by
1/R’ = 2/R+2/R
R’=R/4.
A student made an electric circuit shown here to measure the current through two lamps.
(a) Are the lamps in series or parallel ?
(b) The student has made a mistake in this circuit.
What is the mistake ?
(c) Draw a circuit diagram to show the correct way to connect the circuit.
Use the proper circuit symbols in your diagram.
The electrical resistivities of three materials P, Q and R are given below :
Which material will you use for making (a) electric wires (b) handle for soldering iron, and (c) solar cells ? Give reasons for your choices.
Which of the following equation shows the correct relationship between electrical units ?
1 A = 1 C/s or 1 C = 1 A/s
A resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends ?
The graph between V and 1 for a conductor is a straight line passing through the origin.
Which law is illustrated by such a graph ?
What should remain constant in a statement of this law ?
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
How does the resistance of a wire change when :
(i) its length is tripled ?
(ii) its diameter is tripled ?
(in) its material is changed to one whose resistivity is three times ?
For the circuit shown in the diagram below :
What is the value of :
(i) current through 6 Ωresistor ?
(ii) potential difference across 12 Ω resistor ?
A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
What is an ammeter ? How is it connected in a circuit ? Draw a diagram to illustrate your answer.
In 10 s, a charge of 25 C leaves a battery, and 200 j of energy are delivered to an outside circuit as a result.
(a) What is the p.d. across the battery ?
(b) What current flows from the battery ?
State the factors on which the strength of electric current flowing in a given conductor depends.
If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance ?
Two resistances X and Y are connected turn by turn : (i) in parallel, and (ii) in series. In which case the resultant resistance will be less than either of the individual resistances ?
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
(a) How does the resistance of a pure metal change if its temperature decreases ?
(b) How does the presence of impurities in a metal affect its resistance ?
(a) Give two examples of substances which are good conductors of electricity. Why do you think they are
good conductors of electricity ?
Calculate the resistance of a copper wire 1.0 km long and 0.50 mm diameter if the resistivity of copper is 1.7 × 10-8 Ωm.
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
How much work is done when one coulomb charge moves against a potential difference of 1 volt ?
How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?
If the charge on an electron is 1.6 x 10-19 coulombs, how many electrons should pass through a conductor in 1 second to constitute 1 ampere current ?
What is the general name of the substances having infinitely high electrical resistance ?
Which has less electrical resistance : a thin wire or a thick wire (of the same length and same material) ?
A potential difference of 20 volts is applied across the ends of a resistance of 5 ohms. What current will flow in the resistance ?
Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………
If the length of a wire is doubled by taking more of wire, what happens to its resistance ?
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
If 3 resistances of 3 ohm each are connected in parallel, what will be their total resistance ?
Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.
A wire that has resistance R is cut into two equal pieces. The two parts are joined in parallel. What is the resistance of the combination ?
The circuit diagram given below shows the combination of three resistors R1 R2 and R3 :
Find : (i) total resistance of the circuit.
(ii) total current flowing in the circuit.
(iii) the potential difference across R1.
Which of the following statements correctly defines a volt ?
(a) a volt is a joule per ampere.
(b) a volt is a joule per coulomb.
Fill in the following blanks with suitable words :
(a) Potential difference is measured in………….. by using a……………. placed in………… across a component.
(b) Copper is a good………….. Plastic is an……………
