Electricity (NTSE)

An  electric current of 5 A is the same as:

• 5 JC-1

• 5 VC^-1                 

• 5 Cs^-1           

• 5 Ws^-1

Answer explanation

An electric current of 5 A is equivalent to 5 Cs-1, as 1 A is defined as 1 C/s. Therefore, the correct choice is 5 Cs-1.

If a charged body attracts another body, the charge on the other body :

• must be negative or zero           

• must be positive          

• must be zero 

• may be positive, negative or zero

Answer explanation

A charged body can attract another body with any type of charge. If the other body is neutral (zero charge), it can still be attracted due to polarization. Therefore, the charge on the other body may be positive, negative, or zero.

If the length of a resistance wire is doubled and radius is reduced to half, then the specific resistance of the wire as compared to previous value will be :

• four times             

• eight times            

• half   

• unchanged  

Answer explanation

The specific resistance (resistivity) of a material is an intrinsic property that does not change with dimensions. Therefore, even when the length is doubled and the radius is halved, the specific resistance remains unchanged.

A man has five resistors each of value 1/5 Ω  What is the maximum resistance he can obtain by connecting them?

• 1 Ω                       

• 5 Ω

• ½ Ω             

• 2/5 Ω  

Answer explanation

To achieve maximum resistance, connect the resistors in series. The total resistance is the sum of individual resistances: 1/5 Ω + 1/5 Ω + 1/5 Ω + 1/5 Ω + 1/5 Ω = 1 Ω. Thus, the maximum resistance is 1 Ω.

   Two copper wires, one of length 1m and the other of length 9 m, are found to have the same resistance. Their diameter are in the ratio :

• 3 :1                       

• 1 : 9                       

• 9 :1             

• 1 :3

Answer explanation

Resistance (R) is given by R = ρ(L/A), where A is the cross-sectional area. For equal resistance, R1 = R2 implies ρ1(L1/d1^2) = ρ2(L2/d2^2). Given L1 = 1m, L2 = 9m, we find d1/d2 = sqrt(9) = 3, hence the ratio is 1:3.

A  wire of resistance 6 Ω   is cut into three equal pieces, which are joining to form a triangle. The equivalent resistance between any two comers of the triangle is

• 4/3 Ω                     

• ¾ Ω                      

• 2 Ω               

• 3 Ω

Answer explanation

The total resistance of the wire is 6 Ω. Cutting it into three equal pieces gives each piece a resistance of 2 Ω. In a triangle, the equivalent resistance between any two corners is 4/3 Ω, calculated using the formula for resistors in parallel.

In an electric circuit, ammeter and voltmeter are always connected in

• parallel, series        

• series, parallel        

• series, series         

• parallel, parallel

Answer explanation

In an electric circuit, an ammeter measures current and must be connected in series to measure the same current flowing through the circuit. A voltmeter measures voltage and is connected in parallel to measure the potential difference across components.

The unit of electric power is

• Watt (w)                

• Ampere  (A)           

• Joule (j)            

• Ohm (Ω)

Answer explanation

The unit of electric power is the Watt (W), which measures the rate of energy transfer. Ampere (A) measures current, Joule (J) measures energy, and Ohm (Ω) measures resistance, making Watt the correct choice.

kWh is a unit of :

• Resistance    

• Power  

• electrical energy           

• None

Answer explanation

kWh, or kilowatt-hour, is a unit of electrical energy. It measures the amount of energy consumed over time, specifically the energy used when a power of one kilowatt is maintained for one hour.

How many calories of heat will approximately be developed in a 210 W electric bulb in 5 min?

• 1500

• 1050  

• 63.000                

• 80,000

Answer explanation

To find the heat developed, use the formula: Heat (calories) = Power (W) × Time (s) × 0.239. For 210 W in 5 min (300 s), it equals 210 × 300 × 0.239 ≈ 1500 calories. Thus, the correct answer is 1500.