12. The electric current is due to the flow of-- 
                
             
         
        
                                                                        
                    
                    
                                                                                
                    
                    
                                                                                
                            
                                
                            
                            
                                
                            
                            
                                
                            
                            both positive and negative charges   
                         
                    
                    
                                                                                
                    
                    
                                                         
                    
                            
                    ব্যাখ্যা: ব্যাখ্যাঃ Where there is current, the electrons will Bow in one direction and holes to the other direction. The direction of current flow is defined as the direction of positive charges. But the current flow is the flow of both negative and positive charges.