what if number of advertiser increase for example i am advertising in the web design and if the number of advertiser in web design increase to 1000 and will there be limited space is adwords has a limit of how many advertiser can advertise on adwords and if so will this also increase the minimum cpc.
You want to stay in the top 1000, just be sure your CPC bid or CPM price is in the top 1000. It's not always best to show up #1 for your keyword/phrase. Depending on the demographic you may be paying to have your competition click your ad, to see who they are competing with. Look for buyer keywords (buy xxxx, reviews of xxxx, pricing for xxxx, etc). You may find less competition and higher conversions...
I think that what you mean by minimum CPC is the first page bid estimate. There is no limit to the number of advertisers. Effectively, there is limitless space. There is a limit of how many show per page (8 on right side, 0 to 3 on top of SERPs). As with organic, the first page is where all advertisers want to be because that's the page guaranteed to be seen. So the number of advertisers, whether 10 or 1000 is irrelevant. However, with more advertisers, there are more shooting for that first page. Too many advertisers' idea of getting there is increasing their bid. Thus, as Douglas said, supply and demand: more usually means higher prices. Although I believe there is some saturation point. Going from 10 to 20 advertisers will have a greater effect on price increases than going from 40 to 50 and even less from 90 to 100. If there are 100 advertisers and goes up to 200 overnight, you would not likely notice much of an increase in price, if any. Having many advertisers also means there is a greater chance that more have great QS in the 8 to 10 range. Those with QS of 10 are in the driver seat because they pay about 50% less than advertisers with QS of 7. QS follows a roughly bell-shaped curve. 50% are in the 5 to 7 range, 25% below 5 and 25% above 7. Only about 10% or less have a QS of 10. But if there are a total of 1000 advertisers for a keyword, you are up against 100 for which you have to bid 50% more just to outrank their ad position (if your QS is 7, about 66% more if your QS is 6). Of course, that affects the minimum first page bid. With hundreds of competitors, you can assume that most in the first page have a QS of 10, or close to it. Those are the people in control. They can increase their bid without affecting their costs too much just to keep the ones with lower QS out of the first page.