Answer: (ii) 3.6 x 10

^{4}C

### 21. The resistance of a straight conductor is independent of

(i) temperature

(ii) material

(iii) cross-sectional area

(iv) shape of cross-section

Answer: (iv) shape of cross-section

### 22. A length of wire has a resistance of 6 ohms. The resistance of a wire of the same material three times as long and twice the cross-sectional area will be

(i) 36 ohms

(ii) 9 ohms

(iii) 1 ohm

(iv) 12 ohms

Answer: (ii) 9 ohms

### 23. The drift velocity of electrons is of the order of

(i) 1 ms^{-1}

(ii) 10^{-3} ms^{-1}

(iii)10^{6} ms^{-1}

(iv) 3 x 10^{8 }ms^{-1}

Answer: (ii) 10

^{-3}ms

^{-1}

### 24. Conductivity is the reciprocal of

(i) current density

(ii) resistance

(iii) resistivity

(iv) none of the above

Answer: (iii) resistivity

### 25. The specific resistance of a metallic conductor with rise in temperature

(i) increases

(ii) decreases

(iii) remains unchanged

(iv) none of the above

Answer: (i) increases

### 26. The potential difference of an energy source that provides 50 mJ of energy for every micro coulomb of charge that flows is

(i) 5 V

(iii) 500V

(ii) 50 V

(iv) 50kV

Answer: (iv) 50kV

### 27. Insulators have temperature co-efficient of resistance

(i) zero

(ii) positive

(iii) negative

(iv) none of above

Answer: (iii) negative

## 28. Eureka has ………. temperature co-efficient of resistance.

(i) almost zero

(ii) negative

(iii) positive

(iv) none of the above

Answer: (i) almost zero

### 29. What quantity of charge must be delivered by a battery with a potential difference of 100 V to do 500 J of work ?

(i) 5C

(ii) 0.5C

(iii) 50C

(iv) 500C

Answer: (i) 5C

### 30. A piece of aluminium wire is stretched to reduce its diameter to half of its original value. Its resistance will become

(i) two times

(ii) four times

(iii) eight times

(iv) sixteen times

Answer: (iv) sixteen times

### 31. Semiconductors have temperature coefficient of resistance

(i) zero

(ii) negative

(ii) positive

(iv) none of the above

Answer: (ii) negative

### 32. The thermal speed of electrons is of the order of

(i) 1 ms^{-1}

(ii) 10^{3} ms^{-1}

(iii) 10^{6} ms^{-1}

(iv) 3 x 10^{8} ms^{-1}

Answer: (iii) 10

^{6}ms

^{-1}

### 33. Constantan wire is used for making standard resistance because it has

(i) low specific resistance

(ii) high specific resistance

(iii) negligibly small temperature co-efficient of resistance

(iv) high melting point

Answer: (iii) negligibly small temperature co-efficient of resistance

### 34. The resistance of a material 2 m long and 2 m^{2} in area of x-section is 1.6 x 10^{8 }Ω. Its specific resistance will be

(i) 16 x 10^{-8}

(ii) 6.4 x 10^{-8}

(iii) 3.2 x10^{-8}

(iv) 0.16 x 10^{-8}

Answer: (i) 16 x 10

^{-8}

### 35. The SI unit of conductivity is

(i) ohm-m

(ii) ohm/m

(iii)mho-m

(iv) mho/m

Answer: (iv) mho/m

### 36. The value of α (temperature co-efficient of resistance) depends upon

(i) length of the material

(ii) X-sectional area of the material

(iii) volume of the material

(iv) nature of the material and temperature

Answer: (iv) nature of the material and temperature

### 37. A copper wire of resistance R_{o} is stretched till its length is increased n times of its original length. Its resistance now will be

(i) n^{2}R_{o}

(ii) R_{o}/n^{2}

(iii) nR_{o}

(iv) n^{3}R_{o}

Answer: (i) n

^{2}R

_{o}

### 38. The resistivity of a material is 2 x 10^{-8} Ωm. What will be the resistance of a hollow pipe of the material of length 1 m and having inner and outer radii 10 cm and 20 cm respectively ?

(i) 2 x 10^{-4} Ω

(ii) 2.1 x 10^{-7} Ω

(iii) 3 x 10^{-5 }Ω

(iv) 2.82 x 10^{-3} Ω

Answer: (ii) 2.1 x 10

^{-7}Ω

### 39. A piece of aluminium (Al) and germanium (Ge) are called from T_{i} K to T_{2 }K. The resistance of

(i) each of them increases

(ii) each of them decreases

(iii) aluminium increases and that of germanium decreases

(iv) aluminium decreases and that of germanium increases.

Answer: (iv) aluminium decreases and that of germanium increases.

### 40. At 0 K, germanium behaves as

(i) a conductor

(ii) an insulator

(iii) a superconductor

(iv) a ferromagnetic substance.

Answer: (ii) an insulator