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 Current electricity 

Multiple choice questions

Which of the alternatives, A to E 

1.    is the charge, in coulombs, which passes a point in a circuit in 1 minute when a current of 3 A is flowing?
                                                                             
                

                 C  12 
   
              D  18   
                 
180  

2.    is the potential difference, in volts, required to pass a current of 3 A through a resistor of 6 ohms?
               
A                                                                 
               
B 3       
               
C 12                                 
                D  18      
               
E 180     

Choose the best phrase from the list A to E below to complete each of the sentences in the questions.

    If a resistor is added in parallel with one of equal resistance, the resistance of the combination ___________
                
A increases by a small fraction                                           
                
B decreases by a small fraction       
                
C remains the same                        
                
D is doubled                                                  
                
E is halved                                     

4     If a resistor is added in parallel with one of much smaller resistance, the resistance of the combination ___________
                
A increases by a small fraction                                              
                
B decreases by a small fraction           
                
C remains the same                            
                
D is doubled                                      
                
E is halved                                         

 5     If a resistor is added in series with one of equal resistance, the resistance of the combination
                
A increases by a small fraction                                         
                
B decreases by a small fraction            
                
C remains the same                              
                
D is doubled                                        
                
E is halved                                           

Each of the following questions or incomplete statements is followed by five suggested answers labelled.  Select the best answer in each case.

Four lamps each with a resistance of 6 ohms are connected in parallel to a 12 V battery which has no internal resistance.

6    The current flowing through the battery is 
                A 8A. B 6 A. C 4A. D 2A. E zero.

7    The power consumed by each lamp is 
                A 2W. B6W. C 12W. D 24W. E 72W.

 8    The total charge leaving the battery in 10 seconds is c 
                A 80 C. B 60 C. C 40 C. D 20 C. E zero,

    What is the charge which passes a point in a conductor when a current of 10 mA flows for 50 s?
                
A 0.2 C                                     
               
B 0.5 C   
               
C 5.0 C           
               
D 50 C                        
               
E 500 C         
                                            
                               

10     The e.m.f of a battery is measured in the same units as
                
A force.                                                            
                
B potential difference.      
               
C energy.            
               
D power.    
                E charge.                   

 11     A 6 V battery is made up of four 1.5 V cells, each with an internal resistance of 0.2 ohms connected in series. The greatest current that could possibly be obtained from such a battery is
                 A 0.3 A.                                                             
                
B 0.75 A.          
                
C 3.0 A.                         
                
D 7.5 A.       
                 E 30 A.                    

12    On which one of the following does the electrical resistance of a wire not depend?
      
   the density of the material of the wire
      
    the resistivity of the material of the wire
      
    the length of the wire
      
    the temperature of the wire
      
    the diameter of the wire                           

13    Which of the following changes would increase electrical resistance?
      
    using a shorter wire
      
    using a thinner wire
      
    using a thicker wire
      
D     using wire of lower resistivity
      
E     decreasing the temperature of the wire

14    A pupil makes a resistor from a length of wire. She then makes a second resistor using wire of the same material but of half the diameter and twice the length. The ratio of the value of the second resistor to that of the first is
      
A 1: 8
      
B 1/2.
       C 1.
      
D 2.
      
E 8.       

 15    Figure 24.1 shows a circuit containing a cell and three similar lamps.

       Which of the following statements about the brightness of the lamps is correct?
      
  L1 is brighter than L2 which is brighter than L3.
      
B  L1 is brighter than L2 which has the same brightness as L3
      
C  L1 and L2 have the same brightness, but L3 is less bright.
      
 L3 is brighter than L2 which is brighter than L1.
      
E   L3 is brighter than L2 which has the same brightness as L1. 

Two coils of wire of resistance 2 ohms and 4 ohms are connected in parallel with each other, and a 6 volt battery is connected to this combination.

16    The total resistance of the two coils is
                
A 3/4 ohms.                                                      
                
B 4/3 ohms.          
                
C 2 ohms.                    
                
D 4 ohms.         
                 E 6 ohms.                

17   The current flowing through the 2 ohm coil is
                
A 4.5 A.                                                           
                
B 3 A.            
                
C 1.5 A.                              
                
D 1 A.     
                 E 0.67 A.                          

18   What is the effective resistance between X and Y (see Fig. 24.2)?
                
A 1.2 ohms.                                                      
                
B 5ohms      
                
C 6 ohms                              
                
D 7.5 ohms.        
                 E 12 ohms.               

19    Figure 24.3 shows a circuit containing a cell, a switch and three similar lamps.

       When the switch is closed which of the following statements correctly describes what happens to lamps L1 and L2?
                
L1                                             L2
                
A brighter                                 brighter
                
B brighter                                 the same
                
C brighter                                 dimmer
                
D the same                               dimmer
                
E dimmer                                 dimmer     

20    A 24 watt 12 volt headlamp is fully lit by connecting it to a 12 volt battery. The working resistance of the headlamp is
                
A 1/6 ohms.                                                   
                
B 1/2 ohms.    
                
C 2 ohms.                              
                
D 4 ohms     
                 E 6 ohms.                      

21    What current flows through the headlamp?
                A  2A                                                     
                B  288A                  
                C  4 A                                   
                D  0.5A             
                E   1A              

22   What is the resistance of the element of an electric fire, when it is in use, if it is rated at 2500 W250 V?
       
        A 0.04 ohms                                                   
   
            B  0.1 ohms.                
               C 10 ohms                 
              
D 25 ohms            
               E 250 ohms.          

23    Which of the following quantities do householders pay for when paying the electricity bill?
       
A current                                   
       
B voltage             
       
C power                
       
D energy   
        E resistance        

 Multiple completion questions

For each of the questions, one or more than one of the responses (i), (ii), (iii) (or 1, 2, 3) is/are correct. Select the one letter A, B, C, D, E. which represents the correct responses.

24    Which of the following components has/have the same resistance to electric currents flowing through them in either direction?
           
1 a length of wire
           
2 a variable resistor
           
3 a diode
                
A 1 alone                                  
                
B 3 alone  
                
C l and 2                           
                
D 2 and 3      
                
E 1,2 and 3 
                                           
                

 25    The resistance of a metal wire is reduced by reducing its  
           
1 cross-sectional area.
           
2 length.
           
3 temperature.
                
A 1,2 and 3                                              
                
B 1 and 2              
               
C 2 and 3                             
               
D 1
                E 3 only only                           

 26    Which of the following statements are true of a voltmeter?
  
     1 It has a low resistance.
      
2 It is placed in parallel with a piece of apparatus in a circuit.
      
3 It may have its range increased by the addition of a resistor in series with it.
                
A 1, 2 and 3                                                      
                
B 1 and 2        
                
C 2 and 3                          
                
D 1 only             
                
E 3 only               

27    A circuit is connected up as shown.  The cell has negligible internal resistance.

       When the value of the resistor P is reduced which of the following statements is/are true?
      
(i) The reading of ammeter A l increases.
      
(ii) The reading of ammeter A2 decreases.
      
(iii) The reading of ammeter A3 increases.
                
A (i), (ii) and (iii)                                          
                
B (i) and (ii)                
                
C (i) and (iii)                    
                
D (iii) only          
                 E some other response                

28    The quantity of heat generated in a conductor when a current flows through it is directly proportional to the
      
(i) resistance of the conductor.
      
(ii) current carried by the conductor.
      
(iii) time for which the current flows.
                
A  (i), (ii) and (iii)                                        
                
B  (i) and (ii)
                 
C (i) and (iii) 
    
             D (iii) only
                 E some other response                 

29    An electric lamp is labeled 6 V 0.5 A. When it is operating correctly
      
(i) the power of the lamp is 12 watts.
      
(ii) the resistance of the lamp is 3 ohms.
      
(iii) the energy it consumes in 5 seconds is 15 joules.
                
A (i), (ii) and (iii)                 
                
B (i) and (ii) 
                
C (i) and (iii)   
                 
D (iii) only   
                 E some other response           

30    A 2 kW electrical heater is used continuously. The heater:
      
1 produces 2000 joules of energy every second.
      
2 uses 20 kilowatt-hours of electrical energy in 10 hours.
      
3 passes a current of 8 A when used on 250 V mains.
                
A 1 alone                   
                
B 3 alone                                    
                
C 1 and 2      
                 
D 2 and  3
                
E 1,2 and 3                        

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