EB7 & 8_PRE UPS 2 EB025 22/23

According to the Ohm’s law, the current flow in an electric circuit can be increased by: 

 

 I. Increasing the voltage source 

II. Increasing the resistance 

   III. Decreasing the voltage source 

   IV.    Decreasing the resistance 

• I and II 

• I and IV 

• II and III 

• III and IV 

If

v1=75 sin (ωt− 10°)

 and v2=40 sin (ωt+ 25°), which of these statements are TRUE?  

I. v2 lags v1  

II. v1 lags v2  

III. v1 leads v2  

IV. v2 leads v1  

• I and III 

• II and III 

• II and IV 

• I, III and IV 

Inductive reactance results in a current that 

• Leads the voltage by 90

• Is in phase with the voltage

• Leads the voltage by π rad 

• Lags the voltage by π/2 rad 

If a sinusoidal wave has frequency of 50Hz with 30A rms current, which of the following equation represent the wave? 

• 30 Sin 50t 

• 84.8 Sin 25t 

• 42.42 Sin 314.2t

• 60 Sin 25t 

A phasor is a complex number,

z

that represents the amplitude and phase of sinusoid. The z can be represented as: 

 

I. Rectangular form 

II. Matrix form 

III. Polar form 

• I, II  

• I, III  

• II, III  

• All above 

AC can be produced by a: 

• Transformer 

• Dynamo 

• Electric motor 

• Choke coil 

Which of the following are the advantages provided by Kirchhoff’s law? 

 

I. Solves complex circuits quickly 

II. Unknown voltage values can be calculated 

III. Unknown current values can be calculated 

• I and III 

• I and II 

• II and III 

• All above 

If v1=50 sin (ωt + 10°) and v2=20 sin (ωt − 60°), which of these statements are TRUE?  

I) v1 lags v2  

II) v2 lags v1  

III) v1 leads v2  

IV) v2 leads v1  

• I and III 

• II and III 

• II and IV 

• I, III and IV 

Two resistors with 38 Ω and 42 Ω, respectively are connected in parallel to an unknown current flow. If the voltage source is 35 V, find the overall current flow to the circuit. 

• 1.754 A 

• 4.362 A 

• 6.818 A 

• 8.158 A 

In a pure inductive circuit, if the supply frequency is reduced to ½, the current will? 

• Be reduced by half 

• Be doubled

•  

  Be four times as high 

• Be reduced to one fourth