Providing sufficient base drive current is a key problem in the use of bipolar transistors as switches. The transistor provides current gain, allowing a relatively large current in the collector to be switched by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. In the example light-switch circuit shown, the resistor is chosen to provide enough base current to ensure the transistor will be saturated.
What is a major problem with using bipolar transistors as switches?
Providing sufficient base drive current

Some in the entertainment industry were critical of the star-making aspect of the show. Usher, a mentor on the show, bemoaning the loss of the "true art form of music", thought that shows like American Idol made it seem "so easy that everyone can do it, and that it can happen overnight", and that "television is a lie". Musician Michael Feinstein, while acknowledging that the show had uncovered promising performers, said that American Idol "isn't really about music. It's about all the bad aspects of the music business – the arrogance of commerce, this sense of 'I know what will make this person a star; artists themselves don't know.' " That American Idol is seen to be a fast track to success for its contestants has been a cause of resentment for some in the industry. LeAnn Rimes, commenting on Carrie Underwood winning Best Female Artist in Country Music Awards over Faith Hill in 2006, said that "Carrie has not paid her dues long enough to fully deserve that award". It is a common theme that has been echoed by many others. Elton John, who had appeared as a mentor in the show but turned down an offer to be a judge on American Idol, commenting on talent shows in general, said that "there have been some good acts but the only way to sustain a career is to pay your dues in small clubs".
What singer criticized Carrie Underwood for winning a Country Music Award? 
LeAnn Rimes

Copper is an essential trace element in plants and animals, but not some microorganisms. The human body contains copper at a level of about 1.4 to 2.1 mg per kg of body mass. Stated differently, the RDA for copper in normal healthy adults is quoted as 0.97 mg/day and as 3.0 mg/day. Copper is absorbed in the gut, then transported to the liver bound to albumin. After processing in the liver, copper is distributed to other tissues in a second phase. Copper transport here involves the protein ceruloplasmin, which carries the majority of copper in blood. Ceruloplasmin also carries copper that is excreted in milk, and is particularly well-absorbed as a copper source. Copper in the body normally undergoes enterohepatic circulation (about 5 mg a day, vs. about 1 mg per day absorbed in the diet and excreted from the body), and the body is able to excrete some excess copper, if needed, via bile, which carries some copper out of the liver that is not then reabsorbed by the intestine.
How is copper absorbed in humans?
in the gut